The Caml Light system, release 0.6
Documentation and user's manual
Xavier Leroy
September 1993
Contents
I Getting started 6
1 Installation instructions 7
1.1 The Unix version. . . . . . . . . . . . . . . . . . . . . . . . . 7
1.2 The Macintosh version . . . . . . . . . . . . . . . . . . . . . . 7
1.3 The PC versions . . . . . . . . . . . . . . . . . . . . . . . . . 8
II The Caml Light language reference manual 14
2 The Caml Light language reference manual 15
2.1 Lexical conventions . . . . . . . . . . . . . . . . . . . . . . . 16
2.2 Global names. . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.3 Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.4 Type expressions. . . . . . . . . . . . . . . . . . . . . . . . . 20
2.5 Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.6 Patterns. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.7 Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.8 Global definitions. . . . . . . . . . . . . . . . . . . . . . . . 32
2.9 Directives. . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.10 Module implementations. . . . . . . . . . . . . . . . . . . . . . 33
2.11 Module interfaces . . . . . . . . . . . . . . . . . . . . . . . . 34
3 Language extensions 36
3.1 Streams, parsers, and printers. . . . . . . . . . . . . . . . . . 36
3.2 Range patterns. . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.3 Recursive definitions of values . . . . . . . . . . . . . . . . . 37
3.4 Mutable variant types . . . . . . . . . . . . . . . . . . . . . . 37
3.5 Directives. . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
III The Caml Light library 39
4 The core library 40
4.1 bool: boolean operations . . . . . . . . . . . . . . . . . . . . 40
4.2 builtin: base types and constructors . . . . . . . . . . . . . . 41
4.3 char: character operations . . . . . . . . . . . . . . . . . . . 41
4.4 eq: equality functions . . . . . . . . . . . . . . . . . . . . . 42
4.5 exc: exceptions . . . . . . . . . . . . . . . . . . . . . . . . 42
4.6 fchar: character operations, without sanity checks . . . . . . . 43
4.7 float: operations on floating-point numbers . . . . . . . . . . 43
4.8 fstring: string operations, without sanity checks . . . . . . . 45
4.9 fvect: operations on vectors, without sanity checks . . . . . . 45
4.10 int: operations on integers . . . . . . . . . . . . . . . . . . 45
4.11 io: buffered input and output . . . . . . . . . . . . . . . . . 47
4.12 list: operations on lists . . . . . . . . . . . . . . . . . . . 53
4.13 pair: operations on pairs . . . . . . . . . . . . . . . . . . . 55
4.14 ref: operations on references . . . . . . . . . . . . . . . . . 56
4.15 stream: operations on streams . . . . . . . . . . . . . . . . . 56
1
2
4.16 string: string operations . . . . . . . . . . . . . . . . . . . 57
4.17 vect: operations on vectors . . . . . . . . . . . . . . . . . . 59
5 The standard library 61
5.1 arg: parsing of command line arguments . . . . . . . . . . . . . 61
5.2 baltree: basic balanced binary trees . . . . . . . . . . . . . . 62
5.3 filename: operations on file names . . . . . . . . . . . . . . . 63
5.4 genlex: a generic lexical analyzer . . . . . . . . . . . . . . . 64
5.5 hashtbl: hash tables and hash functions . . . . . . . . . . . . 65
5.6 lexing: the run-time library for lexers generated by camllex . . 66
5.7 map: association tables over ordered types . . . . . . . . . . . 67
5.8 parsing: the run-time library for parsers generated by mlyacc . 68
5.9 printexc: a catch-all exception handler . . . . . . . . . . . . 69
5.10 printf: formatting printing functions . . . . . . . . . . . . . 69
5.11 queue: queues . . . . . . . . . . . . . . . . . . . . . . . . . 70
5.12 random: pseudo-random number generator . . . . . . . . . . . . . 71
5.13 set: sets over ordered types . . . . . . . . . . . . . . . . . . 71
5.14 sort: sorting and merging lists . . . . . . . . . . . . . . . . 72
5.15 stack: stacks . . . . . . . . . . . . . . . . . . . . . . . . . 73
5.16 sys: system interface. . . . . . . . . . . . . . . . . . . . . . 73
6 The graphics library 76
6.1 graphics: machine-independent graphics primitives . . . . . . . 78
IV The Caml Light commands 84
7 Batch compilation (camlc) 85
7.1 Overview of the compiler. . . . . . . . . . . . . . . . . . . . . 85
7.2 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
7.3 Modules and the file system . . . . . . . . . . . . . . . . . . . 88
7.4 Common errors . . . . . . . . . . . . . . . . . . . . . . . . . . 89
8 The toplevel system (camllight) 92
8.1 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
8.2 Toplevel control functions. . . . . . . . . . . . . . . . . . . . 94
8.3 The toplevel and the module system. . . . . . . . . . . . . . . . 96
8.4 Common errors . . . . . . . . . . . . . . . . . . . . . . . . . . 97
8.5 Building custom toplevel systems: camlmktop. . . . . . . . . . . 98
8.6 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
9 The runtime system (camlrun) 100
9.1 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
9.2 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
9.3 Common errors . . . . . . . . . . . . . . . . . . . . . . . . . . 101
10 The librarian (camllibr) 103
10.1 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
10.2 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
10.3 Turning code into a library . . . . . . . . . . . . . . . . . . . 104
11 Lexer and parser generators (camllex, camlyacc) 106
11.1 Overview of camllex . . . . . . . . . . . . . . . . . . . . . . . 106
11.2 Syntax of lexer definitions . . . . . . . . . . . . . . . . . . . 107
11.3 Overview of camlyacc. . . . . . . . . . . . . . . . . . . . . . . 108
11.4 Syntax of grammar definitions . . . . . . . . . . . . . . . . . . 109
11.5 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
11.6 A complete example. . . . . . . . . . . . . . . . . . . . . . . . 111
3
12 Interfacing C with Caml Light 113
12.1 Overview and compilation information. . . . . . . . . . . . . . . 113
12.2 The value type. . . . . . . . . . . . . . . . . . . . . . . . . . 115
12.3 Representation of Caml Light data types . . . . . . . . . . . . . 116
12.4 Operations on values. . . . . . . . . . . . . . . . . . . . . . . 117
12.5 Living in harmony with the garbage collector. . . . . . . . . . . 119
12.6 A complete example. . . . . . . . . . . . . . . . . . . . . . . . 121
V Appendix 124
13 Further reading 125
13.1 Programming in ML . . . . . . . . . . . . . . . . . . . . . . . . 125
13.2 Descriptions of ML dialects . . . . . . . . . . . . . . . . . . . 126
13.3 Implementing functional programming languages . . . . . . . . . . 127
13.4 Applications of ML. . . . . . . . . . . . . . . . . . . . . . . . 128
Foreword
This manual documents the release 0.6 of the Caml Light system. It is
organized as follows.
- Part I, ``Getting started'', explains how to install Caml Light on your
machine.
- Part II, ``The Caml Light language reference manual'', is the reference
description of the Caml Light language.
- Part III, ``The Caml Light library'', describes the modules provided in
the standard library.
- Part IV, ``The Caml Light commands'', documents the Caml Light compiler,
toplevel system, and programming utilities.
- Part V, ``Appendix'', contains a short bibliography, an index of all
identifiers defined in the standard library, and an index of Caml Light
keywords.
Conventions
The Caml Light system comes in several versions: for Unix machines, for
Macintoshes, and for PCs. The parts of this manual that are specific to one
version are presented as shown below:
Unix: This is material specific to the Unix version.
Mac: This is material specific to the Macintosh version.
86: This is material specific to the 8086 (and 80286) PC version.
386: This is material specific to the 80386 PC version.
PC: This is material specific to the two PC versions.
License
c
The Caml Light system is copyright o 1989, 1990. 1991, 1992, 1993 Institut
National de Recherche en Informatique et en Automatique (INRIA). INRIA holds
all ownership rights to the Caml Light system. See the file COPYRIGHT in the
distribution for the copyright notice.
The Caml Light system can be freely copied, but not sold. More precisely,
INRIA grants any user of the Caml Light system the right to reproduce it,
provided that the copies are distributed free of charge and under the
conditions given in the COPYRIGHT file.
4
5
Availability by FTP
The complete Caml Light distribution resides on the machine ftp.inria.fr. The
distribution files can be transferred by anonymous FTP:
Host: ftp.inria.fr (Internet address 192.93.2.54)
Login name: anonymous
Password: your e-mail address
Directory: lang/caml-light
Files: see the index in file README
Part I
Getting started
6
Chapter 1
Installation instructions
This chapter explains how to install Caml Light on your machine.
1.1 The Unix version
Requirements. Any machine that runs under one of the various flavors of the
Unix operating system, and that has a flat, non-segmented, 32-bit or 64-bit
address space. 4M of RAM, 2M of free disk space. The graphics library
requires X11 release 4 or 5.
Installation. The Unix version is distributed in source format, as a
compressed tar file named cl6unix.tar.Z. To extract, move to the directory
where you want the source files to reside, transfer cl6unix.tar.Z to that
directory, and execute
zcat cl6unix.tar.Z | tar xBf -
This extracts the source files in the current directory. The file INSTALL
contains complete instructions on how to configure, compile and install Caml
Light. Read it and follow the instructions.
Troubleshooting. See the file INSTALL.
1.2 The Macintosh version
Requirements. Any Macintosh with at least 1M of RAM (2M is recommended),
running System 6 or 7. About 850K of free space on the disk. The parts of
the Caml Light system that support batch compilation currently require the
Macintosh Programmer's Workshop (MPW) version 3.2. MPW is Apple's development
environment, and it is distributed by APDA, Apple's Programmers and Developers
Association. See the file READ ME in the distribution for APDA's address.
Installation. Create the folder where the Caml Light files will reside.
Double-click on the file cl6macbin.sea from the distribution. This displays a
file dialog box. Open the folder where the Caml Light files will reside, and
click on the Extract button. This will re-create all files from the
distribution in the Caml Light folder.
To test the installation, double-click on the application Caml Light. The
``Caml Light output'' window should display something like
> Caml Light version 0.6
#
7
Chapter 1. Installation instructions 8
In the ``Caml Light input'' window, enter 1+2;; and press the Return key. The
``Caml Light output'' window should display:
> Caml Light version 0.6
#1+2;;
- : int = 3
#
Select ``Quit'' from the ``File'' menu to return to the Finder.
If you have MPW, you can install the batch compilation tools as follows.
The tools and scripts from the tools folder must reside in a place where MPW
will find them as commands. There are two ways to achieve this result:
either copy the files in the tools folder to the Tools or the Scripts folder
in your MPW folder; or keep the files in the tools folder and add the
following line to your UserStartup file (assuming Caml Light resides in folder
Caml Light on the disk named My HD):
Set Commands "{Commands},My HD:Caml Light:tools:"
In either case, you now have to edit the camlc script, and replace the string
Macintosh HD:Caml Light:lib:
(in the first line) with the actual pathname of the lib folder. For example,
if you put Caml Light in folder Caml Light on the disk named My HD, the first
line of camlc should read:
Set stdlib "My HD:Caml Light:lib:"
Troubleshooting. Here is one commonly encountered problem.
Cannot find file stream.zi
(Displayed in the ``Caml Light output'' window, with an alert box telling
you that Caml Light has terminated abnormally.) This is an installation
error. The folder named lib in the distribution must always be in the
same folder as the Caml Light application. It's OK to move the
application to another folder; but remember to move the lib directory to
the same folder. (To return to the Finder, first select ``Quit'' from
the ``File'' menu.)
1.3 The PC versions
Two versions are distributed for the PC. The first one, dubbed ``8086 PC''
here, runs on all PCs, whatever their processor is (8088, 8086, 80286, 80386
DX or SX, 80486 DX or SX, and so on). The second one, dubbed ``80386 PC'',
runs in 32-bit protected mode, and is therefore faster and takes advantage of
memory above the standard 640K, but runs only on PCs with 80386, 80486 or
Pentium processors. The binaries for these two versions are distributed as
two zip archive files cl6pc86bin.zip and cl6pc386bin.zip.
In the following, we assume that the distribution files resides in drive A:,
and that the hard disk on which you are installing Caml Light is drive C:. If
this is not the case, replace A: and C: by the appropriate drives.
Chapter 1. Installation instructions 9
1.3.1 The 8086 PC version
Requirements. A PC running MS-DOS version 3.1 or later. 640K of RAM. About
800K of free space on the disk. The graphics primitives require a CGA, EGA,
or VGA video card.
Installation. Create a directory on the hard disk where Caml Light will
reside. In the following, we assume that this directory is named C:\caml86.
If you choose a different directory, replace C:\caml86 in the following by the
appropriate absolute path name. Then, execute the following commands:
cd C:\caml86
A:pkunzip -d A:cl6pc86
(Be careful not to omit the -d option to pkunzip.) This extracts all files in
the C:\caml86 directory. Then, edit the C:\autoexec.bat file, in order to:
- add C:\caml86\bin to the PATH variable; that is, transform the line that
reads
SET PATH=C:\dos;...
into
SET PATH=C:\dos;...;C:\caml86\bin
- insert the following line
SET CAMLLIB=C:\caml86\lib
Then, save the autoexec.bat file and restart the machine. To test the
installation, execute:
camlc -v
The camlc command should print something like:
The Caml Light system for the 8086 PC, version 0.6
(standard library from C:\caml86\lib)
The Caml Light runtime system, version 0.6
The Caml Light compiler, version 0.6
The Caml Light linker, version 0.6
Then, execute:
caml
The caml command should print something like:
> Caml Light version 0.6
#
Chapter 1. Installation instructions 10
In response to the # prompt, type:
quit();;
This should get you back to the DOS command interpreter.
If you wish to use the graphics primitives, you must install a BGI driver
corresponding to your video card in the C:\caml86\lib directory. You will
need the BGI driver CGA.BGI for a CGA card, EGAVGA.BGI for a VGA or EGA card.
You may also use other BGI drivers, but they must work in 16-color mode:
256-color modes are not supported. The standard BGI drivers are distributed
with Borland's Turbo C/C++ and Turbo Pascal. Just copy the appropriate driver
to the C:\caml86\lib directory.
Troubleshooting. Here are some commonly encountered problems.
Cannot find the bytecode file or camlrun.exe: No such file
The installation has been performed incorrectly. Double-check the
autoexec.bat file for errors in setting the PATH and CAMLLIB variables.
Out of memory
Caml Light barely fits into the ridiculously small memory space provided
by MS-DOS. Hence, you must make sure that as much of the standard 640K of
RAM as possible are free before running Caml Light. As a rule of thumb,
500K of available RAM is the bare minimum; 600K is still far from
sufficient. To free memory, remove as many device drivers (by
suppressing lines in the config.sys file) and TSR programs (by
suppressing lines in the autoexec.bat file) as possible, and restart the
machine. Alternatively, try to load your drivers and TSRs outside of the
standard 640K zone, with the help of memory managers such as QEMM or the
tools in MS-DOS 5 and later. For more details, consult the MS-DOS
documentation or your favorite PC magazine.
1.3.2 The 80386 PC version
Requirements. A PC equipped with a 80386 or 80486 processor, running MS-DOS
version 3.3 or later. 2M of RAM. About 1.2M of free space on the disk. The
graphics primitives require a VGA or SuperVGA video card.
Installation. Create a directory on the hard disk where Caml Light will
reside. In the following, we assume that this directory is named C:\caml386.
If you choose a different directory, replace C:\caml386 in the following by
the appropriate absolute path name. Then, execute the following commands:
cd C:\caml386
A:pkunzip -d A:cl6pc386
(Be careful not to omit the -d option to pkunzip.) This extracts all files in
the C:\caml386 directory.
Select or create a directory where Caml Light will put its temporary files.
Many machines already have a C:\tmp directory for that purpose. If it does
not exist, create it.
For the remainder of the configuration process, you will have to determine
two things:
- does your machine contain floating-point hardware --- that is, a 387
coprocessor, a 486DX (or higher) processor, or a 487SX (co-)processor?
(If you really don't know, assume no floating-point hardware.)
Chapter 1. Installation instructions 11
- what kind of SuperVGA card do you have? Caml Light has graphics
primitives that work on any VGA card in 320x200 pixels, 256 colors, but
it can take advantage of the extra possibilities of various SuperVGA
cards to work at higher resolution. To do so, you must determine which
chipset is used in your SuperVGA card. Re-read the documentation for the
card, then look at the files with extension .GRD or .GRN (the graphics
drivers) in directory C:\caml386\dev, and find one whose name seems to
match the name of the chipset. If you can't determine which graphics
driver to use, don't worry: you'll stick with the default VGA graphics,
that's all.
Now, edit the C:\autoexec.bat file, in order to:
- Add C:\caml386\bin to the PATH variable; that is, transform the line that
reads
SET PATH=C:\dos;...
into
SET PATH=C:\dos;...;C:\caml386\bin
- Insert the following lines
SET CAMLLIB=C:\caml386\lib
SET GO32TMP=C:\tmp
- If your machine has floating-point hardware, insert the following line:
SET GO32=driver C:\caml386\dev\graph.grd gw 640 gh 480
where graph.grd stands for the name of the graphics driver for your
SuperVGA card, as determined above. The 640 and 480 specify the default
graphics resolution to use; you can put 800 and 600, or 1024 and 768
instead, depending on your taste and the capabilities of your card.
If you were unable to determine the correct graphics driver, do not
insert anything, leaving the GO32 variable undefined.
- If your machine has no floating-point hardware, insert the following
line:
SET GO32=emu C:\caml386\dev\emu387
driver C:\caml386\dev\graph.grd gw 640 gh 480
(on a single line; we had to fold the line above for typesetting) where
graph.grd stands for the name of the graphics driver for your SuperVGA
card, as determined above. As explained in the previous item, you can
Chapter 1. Installation instructions 12
choose another default graphics resolution instead of 640 and 480.
If you were unable to determine the correct graphics driver, insert the
following line instead:
SET GO32=emu C:\caml386\dev\emu387
Then, save the autoexec.bat file and restart the machine. To test the
installation, execute:
camlc -v
The camlc command should print something like:
The Caml Light system for the 80386 PC, version 0.6
(standard library from C:\caml386\lib)
The Caml Light runtime system, version 0.6
The Caml Light compiler, version 0.6
The Caml Light linker, version 0.6
Then, execute:
caml
The caml command should print something like:
> Caml Light version 0.6
#
In response to the # prompt, type:
quit();;
This should get you back to the DOS command interpreter.
Troubleshooting. Here are some commonly encountered problems.
Cannot find the bytecode file or camlrun.exe: No such file
The installation has been performed incorrectly. Double-check the
autoexec.bat file for errors in setting the PATH and CAMLLIB variables.
CPU must be a 386 to run this program
Self-explanatory. You'll have to content yourself with the 8086 PC
version.
CPU must be in REAL mode (not V86 mode) to run this program
Ah. That's a tricky one. A number of utility programs switch the 80386
processor to a particular mode, called ``Virtual 86'' or ``V86'' mode,
that prevents 32-bit protected-mode applications like the 80386 PC
version of Caml Light from starting. These programs include:
- device drivers that provide memory management services
- device drivers that provide enhanced debugging possibilities, such as
Chapter 1. Installation instructions 13
tdh386.sys from Turbo Debugger.
The 80386 PC version cannot start when any of these programs is active.
To solve the problem, remove the guilty device drivers from your
config.sys file.
On the other hand, the 80386 PC version knows how to cohabit with
DPMI-compliant or VCPI-compliant environments and memory managers. These
include Windows 3, Desqview, and the EMM386, QEMM386 and 386MAX memory
managers. In the case of EMM386.EXE from the MS-DOS distribution, EMS
must be enabled (do not give it the NOEMS option). If you run the 80386
PC under a VCPI-compliant memory manager, configure the memory manager so
that it allocates at least 1M of EMS, and preferably 2M or more.
Caml Light runs slowly and does a lot of disk accesses
When Caml Light cannot allocate the RAM it requires, it starts paging to
a disk file, which considerably slows down execution. To avoid this,
make sure that at least 1M or memory is available to Caml Light, and
preferably 2M. Caml Light uses XMS memory if you are not running under a
VCPI-compliant memory manager, and EMS memory if you are running under a
VCPI-compliant memory manager. In the latter case, make sure to
configure the memory manager so that it can allocate enough EMS.
Part II
The Caml Light language
reference manual
14
Chapter 2
The Caml Light language reference manual
Foreword
This document is intended as a reference manual for the Caml Light language.
It lists all language constructs, and gives their precise syntax and informal
semantics. It is by no means a tutorial introduction to the language: there
is not a single example. A good working knowledge of the language, as
provided by the companion tutorial Functional programming using Caml Light, is
assumed.
No attempt has been made at mathematical rigor: words are employed with
their intuitive meaning, without further definition. As a consequence, the
typing rules have been left out, by lack of the mathematical framework
required to express them, while they are definitely part of a full formal
definition of the language. The reader interested in truly formal
descriptions of languages from the ML family is referred to The definition of
Standard ML and Commentary on Standard ML, by Milner, Tofte and Harper, MIT
Press.
Warning
Even though there is currently only one implementation of the Caml Light
language, this document carefully distinguishes the language and its
implementation(s). Implementations can provide extra language constructs;
moreover, all points left unspecified in this reference manual can be
interpreted as the language implementor wishes. All these
implementation-dependent features are of course subject to change in future
releases; only the features specified in this reference manual can be relied
upon.
Notations
The syntax of the language is given in BNF-like notation. Terminal symbols
are set in typewriter font (like this). Non-terminal symbols are set in
italic font (like that). Square brackets [...] denote optional components.
Curly brackets {...} denotes zero, one or several repetitions of the enclosed
components. Curly bracket with a trailing plus sign {...}+ denote one or
several repetitions of the enclosed components. Parentheses (...) denote
grouping.
15
Chapter 2. The Caml Light language reference manual 16
2.1 Lexical conventions
Blanks
The following characters are considered as blanks: space, newline, horizontal
tabulation, carriage return, line feed and form feed. Blanks are ignored, but
they separate adjacent identifiers, literals and keywords that would otherwise
be confused as one single identifier, literal or keyword.
Comments
Comments are introduced by the two characters (*, with no intervening blanks,
and terminated by the characters *), with no intervening blanks. Comments are
treated as blank characters. Comments do not occur inside string or character
literals. Nested comments are correctly handled.
Identifiers
ident ::= letter {letter | 0...9 | _}
letter ::= A...Z | a...z
Identifiers are sequences of letters, digits and _ (the underscore
character), starting with a letter. Letters contain at least the 52 lowercase
and uppercase letters from the ASCII set. Implementations can recognize as
letters other characters from the extended ASCII set. Identifiers cannot
contain two adjacent underscore characters (__). Implementation may limit the
number of characters of an identifier, but this limit must be above 256
characters. All characters in an identifier are meaningful.
Integer literals
integer-literal ::= [-] {0...9}+
| [-] (0x | 0X) {0...9 | A...F | a...f}+
| [-] (0o | 0O) {0...7}+
| [-] (0b | 0B) {0...1}+
An integer literal is a sequence of one or more digits, optionally preceded
by a minus sign. By default, integer literals are in decimal (radix 10). The
following prefixes select a different radix:
0x, 0X hexadecimal (radix 16)
0o, 0O octal (radix 8)
0b, 0B binary (radix 2).
(The initial 0 is the digit zero; the O for octal is the letter O.)
Floating-point literals
float-literal ::= [-] {0...9}+ [. {0...9}] [(e | E) [+ | -] {0...9}+]
Floating-point decimals consist in an integer part, a decimal part and an
exponent part. The integer part is a sequence of one or more digits,
optionally preceded by a minus sign. The decimal part is a decimal point
followed by zero, one or more digits. The exponent part is the character e or
E followed by an optional + or - sign, followed by one or more digits. The
decimal part or the exponent part can be omitted, but not both to avoid
ambiguity with integer literals.
Chapter 2. The Caml Light language reference manual 17
Character literals
char-literal ::= ` regular-char `
| ` \ (\ | ` | n | t | b | r) `
| ` \ (0...9) (0...9) (0...9) `
Character literals are delimited by ` (backquote) characters. The two
backquotes enclose either one character different from ` and \, or one of the
escape sequences below:
--------------------------------------------------------
|Sequence|Character denoted |
--------------------------------------------------------
|\\ |backslash (\) |
|\` |backquote (`) |
|\n |newline (LF) |
|\r |return (CR) |
|\t |horizontal tabulation (TAB) |
|\b |backspace (BS) |
|\ddd |the character with ASCII code ddd in decimal |
--------------------------------------------------------
String literals
string-literal ::= " {string-character} "
string-character ::= regular-char
| \ (\ | " | n | t | b | r)
| \ (0...9) (0...9) (0...9)
String literals are delimited by " (double quote) characters. The two
double quotes enclose a sequence of either characters different from " and \,
or escape sequences from the table below:
--------------------------------------------------------
|Sequence|Character denoted |
--------------------------------------------------------
|\\ |backslash (\) |
|\" |double quote (") |
|\n |newline (LF) |
|\r |return (CR) |
|\t |horizontal tabulation (TAB) |
|\b |backspace (BS) |
|\ddd |the character with ASCII code ddd in decimal |
--------------------------------------------------------
16
Implementations must support string literals up to 2 -1 characters in
length (65535 characters).
Keywords
The identifiers below are reserved as keywords, and cannot be employed
otherwise:
and as begin do done downto
else end exception for fun function
if in let match mutable not
of or prefix rec then to
try type value where while with
The following character sequences are also keywords:
Chapter 2. The Caml Light language reference manual 18
# ! != & ( ) * *. + +.
, - -. -> . .( / /. : ::
:= ; ;; < <. <- <= <=. <> <>.
= =. == > >. >= >=. @ [ [|
] ^ _ __ { | |] } '
Ambiguities
Lexical ambiguities are resolved according to the ``longest match'' rule:
when a character sequence can be decomposed into two tokens in several
different ways, the decomposition retained is the one with the longest first
token.
2.2 Global names
Global names are used to denote value variables, value constructors (constant
or non-constant), type constructors, and record labels. Internally, a global
name consists of two parts: the name of the defining module (the module
name), and the name of the global inside that module (the local name). The
two parts of the name must be valid identifiers. Externally, global names
have the following syntax:
global-name ::= ident
| ident __ ident
The form ident __ ident is called a qualified name. The first identifier is
the module name, the second identifier is the local name. The form ident is
called an unqualified name. The identifier is the local name; the module name
is omitted. The compiler infers this module name following the completion
rules given below, therefore transforming the unqualified name into a full
global name.
To complete an unqualified identifier, the compiler checks a list of
modules, the opened modules, to see if they define a global with the same
local name as the unqualified identifier. When one is found, the identifier
is completed into the full name of that global. That is, the compiler takes
as module name the name of an opened module that defines a global with the
same local name as the unqualified identifier. If several modules satisfy
this condition, the one that comes first in the list of opened modules is
selected.
The list of opened modules always includes the module currently being
compiled (checked first). (In the case of a toplevel-based implementation,
this is the module where all toplevel definitions are entered.) It also
includes a number of standard library modules that provide the initial
environment (checked last). In addition, the #open and #close directives can
be used to add or remove modules from that list. The modules added with #open
are checked after the module currently being compiled, but before the initial
standard library modules.
Chapter 2. The Caml Light language reference manual 19
variable ::= global-name
| prefix operator-name
operator-name ::= + | - | * | / | mod | +. | -. | *. | /.
| @ | ^ | ! | := | = | <> | == | != | !
| < | <= | > | <= | <. | <=. | >. | <=.
cconstr ::= global-name
| []
| ()
ncconstr ::= global-name
| prefix ::
typeconstr ::= global-name
label ::= global-name
Depending on the context, global names can stand for global variables
(variable), constant value constructors (cconstr), non-constant value
constructors (ncconst), type constructors (typeconstr), or record labels
(label). For variables and value constructors, special names built with
prefix and an operator name are recognized. The tokens [] and () are also
recognized as built-in constant constructors (the empty list and the unit
value).
The syntax of the language restricts labels and type constructors to appear
in certain positions, where no other kind of global names are accepted. Hence
labels and type constructors have their own name spaces. Value constructors
and value variables live in the same name space: a global name in value
position is interpreted as a value constructor if it appears in the scope of a
type declaration defining that constructor; otherwise, the global name is
taken to be a value variable. For value constructors, the type declaration
determines whether a constructor is constant or not.
2.3 Values
This section describes the kinds of values that are manipulated by Caml Light
programs.
2.3.1 Base values
Integer numbers
30 30
Integer values are integer numbers from -2 to 2 -1, that is -1073741824
to 1073741823. Implementations may support a wider range of integer values.
Floating-point numbers
Floating-point values are numbers in floating-point representation.
Everything about floating-point values is implementation-dependent, including
the range of representable numbers, the number of significant digits, and the
way floating-point results are rounded.
Characters
Character values are represented as 8-bit integers between 0 and 255.
Character codes between 0 and 127 are interpreted following the ASCII
standard. The interpretation of character codes between 128 and 255 is
implementation-dependent.
Chapter 2. The Caml Light language reference manual 20
Character strings
String values are finite sequences of characters. Implementations must
16
support strings up to 2 -1 characters in length (65535 characters).
Implementations may support longer strings.
2.3.2 Tuples
Tuples of values are written (v1,...,vn), standing for the n-tuple of values
14
v1 to vn. Tuples of up to 2 -1 elements (16383 elements) must be
supported, though implementations may support tuples with more elements.
2.3.3 Records
Record values are labeled tuples of values. The record value written
{label1=v1 ;...;labeln =vn} associates the value vi to the record label
14
labeli, for i=1...n. Records with up to 2 -1 fields (16383 fields) must be
supported, though implementations may support records with more fields.
2.3.4 Arrays
Arrays are finite, variable-sized sequences of values of the same type.
14
Arrays of length up to 2 -1 (16383 elements) must be supported, though
implementations may support larger arrays.
2.3.5 Variant values
Variant values are either a constant constructor, or a pair of a non-constant
constructor and a value. The former case is written cconstr; the latter case
is written ncconstr(v), where v is said to be the argument of the non-constant
constructor ncconstr.
The following constants are treated like built-in constant constructors:
false the boolean false
true the boolean true
() the ``unit'' value
[] the empty list
2.3.6 Functions
Functional values are mappings from values to values.
2.4 Type expressions
typexpr ::= ' ident
| ( typexpr )
| typexpr -> typexpr
| typexpr {* typexpr}+
| typeconstr
| typexpr typeconstr
| ( typexpr {, typexpr} ) typeconstr
Chapter 2. The Caml Light language reference manual 21
The table below shows the relative precedences and associativity of
operators and non-closed type constructions. The constructions with higher
precedences come first.
---------------------------------------------
|Operator |Associativity |
---------------------------------------------
|Type constructor application |-- |
|* |-- |
|-> |right |
---------------------------------------------
Type expressions denote types in definitions of data types as well as in
type constraints over patterns and expressions.
Type variables
The type expression ' ident stands for the type variable named ident. In data
type definitions, type variables are names for the data type parameters. In
type constraints, they represent unspecified types that can be instantiated by
any type to satisfy the type constraint.
Parenthesized types
The type expression ( typexpr ) denotes the same type as typexpr.
Function types
The type expression typexpr_1 -> typexpr_2 denotes the type of functions
mapping arguments of type typexpr_1 to results of type typexpr_2.
Tuple types
The type expression typexpr_1 *...* typexpr_n denotes the type of tuples
whose elements belong to types typexpr_1, ...typexpr_n respectively.
Constructed types
Type constructors with no parameter, as in typeconstr, are type expressions.
The type expression typexpr typeconstr, where typeconstr is a type
constructor with one parameter, denotes the application of the unary type
constructor typeconstr to the type typexpr.
The type expression (typexpr_1,...,typexpr_n) typeconstr, where typeconstr
is a type constructor with n parameters, denotes the application of the n-ary
type constructor typeconstr to the types typexpr_1 through typexpr_n.
2.5 Constants
constant ::= integer-literal
| float-literal
| char-literal
| string-literal
| cconstr
The syntactic class of constants comprises literals from the four base types
(integers, floating-point numbers, characters, character strings), and
constant constructors.
Chapter 2. The Caml Light language reference manual 22
2.6 Patterns
pattern ::= ident
| _
| pattern as ident
| ( pattern )
| ( pattern : typexpr )
| pattern | pattern
| constant
| ncconstr pattern
| pattern , pattern {, pattern}
| { label = pattern {; label = pattern} }
| [ ]
| [ pattern {; pattern} ]
| pattern :: pattern
The table below shows the relative precedences and associativity of
operators and non-closed pattern constructions. The constructions with higher
precedences come first.
----------------------------------------
|Operator |Associativity |
----------------------------------------
|Constructor application|-- |
|:: |right |
|, |-- |
|| |left |
|as |-- |
----------------------------------------
Patterns are templates that allow selecting data structures of a given
shape, and binding identifiers to components of the data structure. This
selection operation is called pattern matching; its outcome is either ``this
value does not match this pattern'', or ``this value matches this pattern,
resulting in the following bindings of identifiers to values''.
Variable patterns
A pattern that consists in an identifier matches any value, binding the
identifier to the value. The pattern _ also matches any value, but does not
bind any identifier.
Alias patterns
The pattern pattern_1 as ident matches the same values as pattern_1. If the
matching against pattern_1 is successful, the identifier ident is bound to the
matched value, in addition to the bindings performed by the matching against
pattern_1.
Parenthesized patterns
The pattern ( pattern_1 ) matches the same values as pattern_1. A type
constraint can appear in a parenthesized patterns, as in ( pattern_1 :
typexpr ). This constraint forces the type of pattern_1 to be compatible with
type.
``Or'' patterns
The pattern pattern_1 | pattern_2 represents the logical ``or'' of the two
patterns pattern_1 and pattern_2. A value matches pattern_1 | pattern_2
either if it matches pattern_1 or if it matches pattern_2. The two
Chapter 2. The Caml Light language reference manual 23
sub-patterns pattern_1 and pattern_2 must contain no identifiers. Hence no
bindings are returned by matching against an ``or'' pattern.
Constant patterns
A pattern consisting in a constant matches the values that are equal to this
constant.
Variant patterns
The pattern ncconstr pattern_1 matches all variants whose constructor is equal
to ncconstr, and whose argument matches pattern_1.
The pattern pattern_1 :: pattern_2 matches non-empty lists whose heads
match pattern_1, and whose tails match pattern_2. This pattern behaves like
prefix :: ( pattern_1 , pattern_2 ).
The pattern [ pattern_1 ;...; pattern_n ] matches lists of length n whose
elements match pattern_1 ...pattern_n, respectively. This pattern behaves
like pattern_1 ::...:: pattern_n :: [].
Tuple patterns
The pattern pattern_1 ,..., pattern_n matches n-tuples whose components match
the patterns pattern_1 through pattern_n. That is, the pattern matches the
tuple values (v1,...,vn) such that pattern_i matches v_i for i =1,..., n.
Record patterns
The pattern { label_1 = pattern_1 ;...; label_n = pattern_n } matches
records that define at least the labels label_1 through label_n, and such that
the value associated to label_i match the pattern pattern_i, for i=1, ...,n.
The record value can define more labels than label_1 ...label_n; the values
associated to these extra labels are not taken into account for matching.
Chapter 2. The Caml Light language reference manual 24
2.7 Expressions
expr ::= ident
| variable
| constant
| ( expr )
| begin expr end
| ( expr : typexpr )
| expr , expr {, expr}
| ncconstr expr
| expr :: expr
| [ expr {; expr} ]
| [| expr {; expr} |]
| { label = expr {; label = expr} }
| expr expr
| prefix-op expr
| expr infix-op expr
| expr . label
| expr . label <- expr
| expr .( expr )
| expr .( expr ) <- expr
| expr & expr
| expr or expr
| if expr then expr [else expr]
| while expr do expr done
| for ident = expr (to | downto) expr do expr done
| expr ; expr
| match expr with simple-matching
| fun multiple-matching
| function simple-matching
| try expr with simple-matching
| let [rec] let-binding {and let-binding} in expr
simple-matching ::= pattern -> expr {| pattern -> expr}
multiple-matching ::= pattern-list -> expr {| pattern-list -> expr}
pattern-list ::= pattern {pattern}
let-binding ::= pattern = expr
| variable pattern-list = expr
prefix-op ::= - | -. | !
infix-op ::= + | - | * | / | mod | +. | -. | *. | /. | @ | ^ | ! | :=
| = | <> | == | != | < | <= | > | <= | <. | <=. | >. | <=.
The table below shows the relative precedences and associativity of
operators and non-closed constructions. The constructions with higher
precedence come first.
Chapter 2. The Caml Light language reference manual 25
---------------------------------------------
|Construction or operator |Associativity |
---------------------------------------------
|! |-- |
|. .( |-- |
|function application |right |
|constructor application |-- |
|- -. (prefix) |-- |
|mod |left |
|* *. / /. |left |
|+ +. - -. |left |
|:: |right |
|@ ^ |right |
|comparisons (= == < etc.) |left |
|not |-- |
|& |left |
|or |left |
|, |-- |
|<- := |right |
|if |-- |
|; |right |
|let match fun function try |-- |
---------------------------------------------
2.7.1 Simple expressions
Constants
Expressions consisting in a constant evaluate to this constant.
Variables
Expressions consisting in a variable evaluate to the value bound to this
variable in the current evaluation environment. The variable can be either a
qualified identifier or a simple identifier. Qualified identifiers always
denote global variables. Simple identifiers denote either a local variable,
if the identifier is locally bound, or a global variable, whose full name is
obtained by qualifying the simple identifier, as described in section 2.2.
Parenthesized expressions
The expressions ( expr ) and begin expr end have the same value as expr. Both
constructs are semantically equivalent, but it is good style to use
begin...end inside control structures:
if ... then begin ... ; ... end else begin ... ; ... end
and (...) for the other grouping situations.
Parenthesized expressions can contain a type constraint, as in ( expr : type
). This constraint forces the type of expr to be compatible with type.
Function abstraction
The most general form of function abstraction is:
1 m
fun pattern1 ... pattern1 -> expr1
| ... 1 m
| patternn ... patternn -> exprn
Chapter 2. The Caml Light language reference manual 26
This expression evaluates to a functional value with m curried arguments.
When this function is applied to m values v1...vm, the values are matched
1 m
against each pattern row patterni ... patterni, for i from 1 to n. If one of
these matchings succeeds, that is if the value vj matches the pattern
j
patterni for all j=1...m, then the expression expri associated to the
selected pattern row is evaluated, and its value becomes the value of the
function application. The evaluation of expri takes place in an environment
enriched by the bindings performed during the matching.
If several pattern rows match the arguments, the one that occurs first in
the function definition is selected. If none of the pattern rows matches the
argument, the exception Match_failure is raised.
If the function above is applied to less than m arguments, a functional
value is returned, that represents the partial application of the function to
the provided arguments. This partial application is a function that, when
applied to the remaining arguments, matches all arguments against the pattern
rows as described above. Matching does not start until all m arguments have
been provided to the function; hence, partial applications of the function to
less than m arguments never raise Match_failure.
All pattern rows in the function body must contain the same number of
patterns. A variable must not be bound more than once in one pattern row.
Functions with only one argument can be defined with the function keyword
instead of fun:
function pattern1 -> expr1
| ...
| patternn -> exprn
The function thus defined behaves exactly as described above. The only
difference between the two forms of function definition is how a parsing
ambiguity is resolved. The two forms cconstr pattern (two patterns in a row)
and ncconstr pattern (one pattern) cannot be distinguished syntactically.
Function definitions introduced by fun resolve the ambiguity to the former
form; function definitions introduced by function resolve it to the latter
form (the former form makes no sense in this case).
Function application
Function application is denoted by juxtaposition of expressions. The
expression expr_1 expr_2 ...expr_n evaluates the expressions expr_1 to
expr_n. The expression expr_1 must evaluate to a functional value, which is
then applied to the values of expr_2, ..., expr_n. The order in which the
expressions expr_1, ..., expr_n are evaluated is not specified.
Local definitions
The let and let rec constructs bind variables locally. The construct
let pattern_1 = expr_1 and...and pattern_n = expr_n in expr
evaluates expr_1 ...expr_n in some unspecified order, then matches their
values against the patterns pattern_1 ...pattern_n. If the matchings succeed,
expr is evaluated in the environment enriched by the bindings performed during
matching, and the value of expr is returned as the value of the whole let
expression. If one of the matchings fails, the exception Match_failure is
raised.
An alternate syntax is provided to bind variables to functional values:
Chapter 2. The Caml Light language reference manual 27
instead of writing
ident = fun pattern_1 ...pattern_m -> expr
in a let expression, one may instead write
ident pattern_1 ...pattern_m = expr
Both forms bind ident to the curried function with m arguments and only one
case,
pattern_1 ...pattern_m -> expr.
Recursive definitions of variables are introduced by let rec:
let rec pattern_1 = expr_1 and...and pattern_n = expr_n in expr
The only difference with the let construct described above is that the
bindings of variables to values performed by the pattern-matching are
considered already performed when the expressions expr_1 to expr_n are
evaluated. That is, the expressions expr_1 to expr_n can reference
identifiers that are bound by one of the patterns pattern_1, ..., pattern_n,
and expect them to have the same value as in expr, the body of the let rec
construct.
The recursive definition is guaranteed to behave as described above if the
expressions expr_1 to expr_n are function definitions (fun... or
function...), and the patterns pattern_1 ...pattern_n consist in a single
variable, as in:
let rec ident_1 = fun...and...and ident_n = fun...in expr
This defines ident_1 ...ident_n as mutually recursive functions local to expr.
The behavior of other forms of let rec definitions is
implementation-dependent.
2.7.2 Control constructs
Sequence
The expression expr_1 ; expr_2 evaluates expr_1 first, then expr_2, and
returns the value of expr_2.
Conditional
The expression if expr_1 then expr_2 else expr_3 evaluates to the value of
expr_2 if expr_1 evaluates to the boolean true, and to the value of expr_3 if
expr_1 evaluates to the boolean false.
The else expr_3 part can be omitted, in which case it defaults to else ().
Case expression
The expression
match expr
with pattern1 -> expr1
| ...
| patternn -> exprn
Chapter 2. The Caml Light language reference manual 28
matches the value of expr against the patterns pattern_1 to pattern_n. If the
matching against pattern_i succeeds, the associated expression expr_i is
evaluated, and its value becomes the value of the whole match expression. The
evaluation of expr_i takes place in an environment enriched by the bindings
performed during matching. If several patterns match the value of expr, the
one that occurs first in the match expression is selected. If none of the
patterns match the value of expr, the exception Match_failure is raised.
Boolean operators
The expression expr_1 & expr_2 evaluates to true if both expr_1 and expr_2
evaluate to true; otherwise, it evaluates to false. The first component,
expr_1, is evaluated first. The second component, expr_2, is not evaluated if
the first component evaluates to false. Hence, the expression expr_1 &
expr_2 behaves exactly as
if expr1 then expr2 else false.
The expression expr_1 or expr_2 evaluates to true if one of expr_1 and
expr_2 evaluates to true; otherwise, it evaluates to false. The first
component, expr_1, is evaluated first. The second component, expr_2, is not
evaluated if the first component evaluates to true. Hence, the expression
expr_1 or expr_2 behaves exactly as
if expr1 then true else expr2.
Loops
The expression while expr_1 do expr_2 done repeatedly evaluates expr_2 while
expr_1 evaluates to true. The loop condition expr_1 is evaluated and tested
at the beginning of each iteration. The whole while...done expression
evaluates to the unit value ().
The expression for ident = expr_1 to expr_2 do expr_3 done first
evaluates the expressions expr_1 and expr_2 (the boundaries) into integer
values n and p. Then, the loop body expr_3 is repeatedly evaluated in an
environment where the local variable named ident is successively bound to the
values n, n+1, ..., p -1, p. The loop body is never evaluated if n> p.
The expression for ident = expr_1 downto expr_2 do expr_3 done first
evaluates the expressions expr_1 and expr_2 (the boundaries) into integer
values n and p. Then, the loop body expr_3 is repeatedly evaluated in an
environment where the local variable named ident is successively bound to the
values n, n-1, ..., p +1, p. The loop body is never evaluated if n< p.
In both cases, the whole for expression evaluates to the unit value ().
Exception handling
The expression
try expr
with pattern1 -> expr1
| ...
| patternn -> exprn
evaluates the expression expr and returns its value if the evaluation of expr
does not raise any exception. If the evaluation of expr raises an exception,
the exception value is matched against the patterns pattern_1 to pattern_n.
If the matching against pattern_i succeeds, the associated expression expr_i
is evaluated, and its value becomes the value of the whole try expression.
Chapter 2. The Caml Light language reference manual 29
The evaluation of expr_i takes place in an environment enriched by the
bindings performed during matching. If several patterns match the value of
expr, the one that occurs first in the try expression is selected. If none of
the patterns matches the value of expr, the exception value is raised again,
thereby transparently ``passing through'' the try construct.
2.7.3 Operations on data structures
Products
The expression expr_1 ,..., expr_n evaluates to the n-tuple of the values of
expressions expr_1 to expr_n. The evaluation order for the subexpressions is
not specified.
Variants
The expression ncconstr expr evaluates to the variant value whose constructor
is ncconstr, and whose argument is the value of expr.
For lists, some syntactic sugar is provided. The expression expr_1 ::
expr_2 stands for the constructor prefix :: applied to the argument ( expr_1
, expr_2 ), and therefore evaluates to the list whose head is the value of
expr_1 and whose tail is the value of expr_2. The expression [ expr_1 ;...;
expr_n ] is equivalent to expr_1 ::...:: expr_n :: [], and therefore
evaluates to the list whose elements are the values of expr_1 to expr_n.
Records
The expression { label_1 = expr_1 ;...; label_n = expr_n } evaluates to
the record value {label1=v1 ;...;labeln =vn}, where vi is the value of expr_i
for i=1, ...,n. The labels label_1 to label_n must all belong to the same
record types; all labels belonging to this record type must appear exactly
once in the record expression, though they can appear in any order. The order
in which expr_1 to expr_n are evaluated is not specified.
The expression expr_1 . label evaluates expr_1 to a record value, and
returns the value associated to label in this record value.
The expression expr_1 . label <- expr_2 evaluates expr_1 to a record value,
which is then modified in-place by replacing the value associated to label in
this record by the value of expr_2. This operation is permitted only if label
has been declared mutable in the definition of the record type. The whole
expression expr_1 . label <- expr_2 evaluates to the unit value ().
Arrays
The expression [| expr_1 ;...; expr_n |] evaluates to a n-element array,
whose elements are initialized with the values of expr_1 to expr_n
respectively. The order in which these expressions are evaluated is
unspecified.
The expression expr_1 .( expr_2 ) is equivalent to the application
vect_item expr_1 expr_2. In the initial environment, the identifier
vect_item resolves to a built-in function that returns the value of element
number expr_2 in the array denoted by expr_1. The first element has number 0;
the last element has number n-1, where n is the size of the array. The
exception Invalid_argument is raised if the access is out of bounds.
The expression expr_1 .( expr_2 ) <- expr_3 is equivalent to vect_assign
expr_1 expr_2 expr_3. In the initial environment, the identifier
vect_assign resolves to a built-in function that modifies in-place the array
denoted by expr_1, replacing element number expr_2 by the value of expr_3.
The exception Invalid_argument is raised if the access is out of bounds. The
Chapter 2. The Caml Light language reference manual 30
built-in function returns (). Hence, the whole expression expr_1 .( expr_2
) <- expr_3 evaluates to the unit value ().
This behavior of the two constructs expr_1 .( expr_2 ) and expr_1 .(
expr_2 ) <- expr_3 may change if the meaning of the identifiers vect_item and
vect_assign is changed, either by redefinition or by modification of the list
of opened modules. See the discussion below on operators.
2.7.4 Operators
The operators written infix-op in the grammar above can appear in infix
position (between two expressions). The operators written prefix-op in the
grammar above can appear in prefix position (in front of an expression).
The expression prefix-op expr is interpreted as the application ident expr,
where ident is the identifier associated to the operator prefix-op in the
table below. Similarly, the expression expr_1 infix-op expr_2 is interpreted
as the application ident expr_1 expr_2, where ident is the identifier
associated to the operator infix-op in the table below. The identifiers
written ident above are then evaluated following the rules in section 2.7.1.
In the initial environment, they evaluate to built-in functions whose behavior
is described in the table. The behavior of the constructions prefix-op expr
and expr_1 infix-op expr_2 may change if the meaning of the identifiers
associated to prefix-op or infix-op is changed, either by redefinition of the
identifiers, or by modification of the list of opened modules, through the
#open and #close directives.
Chapter 2. The Caml Light language reference manual 31
--------------------------------------------------------------------------
|Operator |Associated |Behavior in the default environment |
| |identifier | |
--------------------------------------------------------------------------
|+ |prefix + |Integer addition. |
|- (infix) |prefix - |Integer subtraction. |
|- (prefix) |minus |Integer negation. |
|* |prefix * |Integer multiplication. |
|/ |prefix / |Integer division. Raise Division_by_zero if |
| | |second argument is null. The result is |
| | |unspecified if either argument is negative. |
|mod |prefix mod |Integer modulus. Raise Division_by_zero if |
| | |second argument is null. The result is |
| | |unspecified if either argument is negative. |
|+. |prefix +. |Floating-point addition. |
|-. (infix) |prefix -. |Floating-point subtraction. |
|-. (prefix)|minus_float |Floating-point negation. |
|*. |prefix *. |Floating-point multiplication. |
|/. |prefix /. |Floating-point division. The result is |
| | |unspecified if second argument is null. |
|@ |prefix @ |List concatenation. |
|^ |prefix ^ |String concatenation. |
|! |prefix ! |Dereferencing (return the current contents of |
| | |a reference). |
|:= |prefix := |Reference assignment (update the reference |
| | |given as first argument with the value of the |
| | |second argument). |
|= |prefix = |Structural equality test. |
|<> |prefix <> |Structural inequality test. |
|== |prefix == |Physical equality test. |
|!= |prefix != |Physical inequality test. |
|< |prefix < |Test ``less than'' on integers. |
|<= |prefix <= |Test ``less than or equal '' on integers. |
|> |prefix > |Test ``greater than'' on integers. |
|>= |prefix >= |Test ``greater than or equal'' on integers. |
|<. |prefix <. |Test ``less than'' on floating-point numbers. |
|<=. |prefix <=. |Test ``less than or equal '' on floating-point |
| | |numbers. |
|>. |prefix >. |Test ``greater than'' on floating-point |
| | |numbers. |
|>=. |prefix >=. |Test ``greater than or equal'' on floating- |
| | |point numbers. |
--------------------------------------------------------------------------
The behavior of the +, -, *, /, mod, +., -., *. or /. operators is
unspecified if the result falls outside of the range of representable integers
or floating-point numbers, respectively. See chapter 4 for a more precise
description of the behavior of the operators above.
Chapter 2. The Caml Light language reference manual 32
2.8 Global definitions
This section describes the constructs that bind global identifiers (value
variables, value constructors, type constructors, record labels).
2.8.1 Type definitions
type-definition ::= type typedef {and typedef}
typedef ::= type-params ident = constr-decl {| constr-decl}
| type-params ident = { label-decl {; label-decl} }
| type-params ident == typexpr
| type-params ident
type-params ::= nothing
| ' ident
| ( ' ident {, ' ident} )
constr-decl ::= ident
| ident of typexpr
label-decl ::= ident : typexpr
| mutable ident : typexpr
Type definitions bind type constructors to data types: either variant
types, record types, type abbreviations, or abstract data types.
Type definitions are introduced by the type keyword, and consist in one or
several simple definitions, possibly mutually recursive, separated by the and
keyword. Each simple definition defines one type constructor.
A simple definition consists in an identifier, possibly preceded by one or
several type parameters, and followed by a data type description. The
identifier is the local name of the type constructor being defined. (The
module name for this type constructor is the name of the module being
compiled.) The optional type parameters are either one type variable ' ident,
for type constructors with one parameter, or a list of type variables ('
ident_1,...,' ident_n), for type constructors with several parameters. These
type parameters can appear in the type expressions of the right-hand side of
the definition.
Variant types
The type definition typeparams ident = constr-decl_1 |...| constr-decl_n
defines a variant type. The constructor declarations constr-decl_1, ...,
constr-decl_n describe the constructors associated to this variant type. The
constructor declaration ident of typexpr declares the local name ident (in the
module being compiled) as a non-constant constructor, whose argument has type
typexpr. The constructor declaration ident declares the local name ident (in
the module being compiled) as a constant constructor.
Record types
The type definition typeparams ident = { label-decl_1 ;...; label-decl_n }
defines a record type. The label declarations label-decl_1, ..., label-decl_n
describe the labels associated to this record type. The label declaration
ident : typexpr declares the local name ident in the module being compiled as
a label, whose argument has type typexpr. The label declaration mutable ident
: typexpr behaves similarly; in addition, it allows physical modification over
the argument to this label.
Chapter 2. The Caml Light language reference manual 33
Type abbreviations
The type definition typeparams ident == typexpr defines the type constructor
ident as an abbreviation for the type expression typexpr.
Abstract types
The type definition typeparams ident defines ident as an abstract type. When
appearing in a module interface, this definition allows exporting a type
constructor while hiding how it is represented in the module implementation.
2.8.2 Exception definitions
exception-definition ::= exception constr-decl {and constr-decl}
Exception definitions add new constructors to the built-in variant type exn
of exception values. The constructors are declared as for a definition of a
variant type.
2.9 Directives
directive ::= # open string
| # close string
| # ident string
Directives control the behavior of the compiler. They apply to the
remainder of the current compilation unit.
The two directives #open and #close modify the list of opened modules, that
the compiler uses to complete unqualified identifiers, as described in
section 2.2. The directive #open string adds the module whose name is given
by the string constant string to the list of opened modules, in first
position. The directive #close string removes the first occurrence of the
module whose name is given by the string constant string from the list of
opened modules.
Implementations can provide other directives, provided they follow the
syntax # ident string, where ident is the name of the directive, and the
string constant string is the argument to the directive. The behavior of
these additional directives is implementation-dependent.
2.10 Module implementations
implementation ::= {impl-phrase ;;}
impl-phrase ::= expr
| value-definition
| type-definition
| exception-definition
| directive
value-definition ::= let [rec] let-binding {and let-binding}
A module implementation consists in a sequence of implementation phrases,
terminated by double semicolons. An implementation phrase is either an
expression, a value definition, a type or exception definition, or a
directive. At run-time, implementation phrases are evaluated sequentially, in
the order in which they appear in the module implementation.
Implementation phrases consisting in an expression are evaluated for their
side-effects.
Chapter 2. The Caml Light language reference manual 34
Value definitions bind global value variables in the same way as a
let...in... expression binds local variables. The expressions are evaluated,
and their values are matched against the left-hand sides of the = sides, as
explained in section 2.7.1. If the matching succeeds, the bindings of
identifiers to values performed during matching are interpreted as bindings to
the global value variables whose local name is the identifier, and whose
module name is the name of the module. If the matching fails, the exception
Match_failure is raised. The scope of these bindings is the phrases that
follow the value definition in the module implementation.
Type and exception definitions introduce type constructors, variant
constructors and record labels as described in sections 2.8.1 and 2.8.2. The
scope of these definitions is the phrases that follow the value definition in
the module implementation. The evaluation of an implementation phrase
consisting in a type or exception definition produces no effect at run-time.
Directives modify the behavior of the compiler on the subsequent phrases of
the module implementation, as described in section 2.9. The evaluation of an
implementation phrase consisting in a directive produces no effect at
run-time. Directives apply only to the module currently being compiled; in
particular, they have no effect on other modules that refer to globals
exported by the module being compiled.
2.11 Module interfaces
interface ::= {intf-phrase ;;}
intf-phrase ::= value-declaration
| type-definition
| exception-definition
| directive
value-declaration ::= value ident : typexpr {and ident : typexpr}
Module interfaces declare the global objects (value variables, type
constructors, variant constructors, record labels) that a module exports, that
is, makes available to other modules. Other modules can refer to these
globals using qualified identifiers or the #open directive, as explained in
section 2.2.
A module interface consists in a sequence of interface phrases, terminated
by double semicolons. An interface phrase is either a value declaration, a
type definition, an exception definition, or a directive.
Value declarations declare global value variables that are exported by the
module implementation, and the types with which they are exported. The module
implementation must define these variables, with types at least as general as
the types declared in the interface. The scope of the bindings for these
global variables extends from the module implementation itself to all modules
that refer to those variables.
Type or exception definitions introduce type constructors, variant
constructors and record labels as described in sections 2.8.1 and 2.8.2.
Exception definitions and type definitions that are not abstract type
declarations also take effect in the module implementation; that is, the type
constructors, variant constructors and record labels they define are
considered bound on entrance to the module implementation, and can be referred
to by the implementation phrases. Type definitions that are not abstract type
declarations must not be redefined in the module implementation. In contrast,
the type constructors that are declared abstract in a module interface must be
defined in the module implementation, with the same names.
Directives modify the behavior of the compiler on the subsequent phrases of
the module interface, as described in section 2.9. Directives apply only to
the interface currently being compiled; in particular, they have no effect on
Chapter 2. The Caml Light language reference manual 35
other modules that refer to globals exported by the interface being compiled.
Chapter 3
Language extensions
This chapter describes the language features that are implemented in Caml
Light, but not described in the Caml Light reference manual. In contrast with
the fairly stable kernel language that is described in the reference manual,
the extensions presented here are still experimental, and may be removed or
changed in the future.
3.1 Streams, parsers, and printers
Caml Light comprises a built-in type for streams (possibly infinite sequences
of elements, that are evaluated on demand), and associated stream expressions,
to build streams, and stream patterns, to destructure streams. Streams and
stream patterns provide a natural approach to the writing of recursive-descent
parsers.
Streams are presented by the following extensions to the syntactic classes
of expressions:
expr ::= ...
| [< >]
| [< stream-component {; stream-component} >]
| function stream-pattern -> expr {| stream-pattern -> expr}
| match expr with stream-pattern -> expr {| stream-pattern -> expr}
stream-component ::= ' expr
| expr
stream-pattern ::= [< >]
| [< stream-comp-pat {; stream-comp-pat} >]
stream-comp-pat ::= ' pattern
| expr pattern
| ident
Stream expressions are bracketed by [< and >]. They represent the
concatenation of their components. The component ' expr represents the
one-element stream whose element is the value of expr. The component expr
represents a sub-stream. For instance, if both s and t are streams of
integers, then [<'1; s; t; '2>] is a stream of integers containing the element
1, then the elements of s, then those of t, and finally 2. The empty stream
is denoted by [< >].
Unlike any other kind of expressions in the language, stream expressions are
submitted to lazy evaluation: the components are not evaluated when the
stream is built, but only when they are accessed during stream matching. The
components are evaluated once, the first time they are accessed; the following
accesses reuse the value computed the first time.
36
Chapter 3. Language extensions 37
Stream patterns, also bracketed by [< and >], describe initial segments of
streams. In particular, the stream pattern [< >] matches all streams. Stream
pattern components are matched against the corresponding elements of a stream.
The component ' pattern matches the corresponding stream element against the
pattern. The component expr pattern applies the function denoted by expr to
the current stream, then matches the result of the function against pattern.
Finally, the component ident simply binds the identifier to the stream being
matched. (The current implementation limits ident to appear last in a stream
pattern.)
Stream matching proceeds destructively: once a component has been matched,
it is discarded from the stream (by in-place modification).
Stream matching proceeds in two steps: first, a pattern is selected by
matching the stream against the first components of the stream patterns; then,
the following components of the selected pattern are checked against the
stream. If the following components do not match, the exception Parse_error
is raised. There is no backtracking here: stream matching commits to the
pattern selected according to the first element. If none of the first
components of the stream patterns match, the exception Parse_failure is
raised. The Parse_failure exception causes the next alternative to be tried,
if it occurs during the matching of the first element of a stream, before
matching has committed to one pattern.
See Functional programming using Caml Light for a more gentle introductions
to streams, and for some examples of their use in writing parsers. A more
formal presentation of streams, and a discussion of alternate semantics, can
be found in Parsers in ML by Michel Mauny and Daniel de Rauglaudre, in the
proceedings of the 1992 ACM conference on Lisp and Functional Programming.
3.2 Range patterns
In patterns, Caml Light recognizes the form ` c ` .. ` d ` (two character
constants separated by ..) as a shorthand for the pattern
` c ` | ` c_1 ` | ` c_2 ` |...| ` c_n ` | ` d `
where c1,c2,...,cn are the characters that occur between c and d in the
ASCII character set. For instance, the pattern `0`..`9` matches all
characters that are digits.
3.3 Recursive definitions of values
Besides let rec definitions of functional values, as described in the
reference manual, Caml Light supports a certain class of recursive definitions
of non-functional values. For instance, the following definition is accepted:
let rec x = 1 :: y and y = 2 :: x;;
and correctly binds x to the cyclic list 1::2 ::1 ::2 ::..., and y to the
cyclic list 2::1 ::2 ::1 ::... Informally, the class of accepted definitions
consists of those definitions where the defined variables occur only inside
function bodies or as a field of a data structure. Moreover, the patterns in
the left-hand sides must be identifiers, nothing more complex.
3.4 Mutable variant types
The argument of a value constructor can be declared ``mutable'' when the
variant type is defined:
Chapter 3. Language extensions 38
type foo = A of mutable int
| B of mutable int * int
| ...
This allows in-place modification of the argument part of a constructed value.
Modification is performed by a new kind of expressions, written ident <- expr,
where ident is an identifier bound by pattern-matching to the argument of a
mutable constructor, and expr denotes the value that must be stored in place
of that argument. Continuing the example above:
let x = A 1 in
begin match x with A y -> y <- 2 | _ -> () end;
x
returns the value A 2. The notation ident <- expr works also if ident is an
identifier bound by pattern-matching to the value of a mutable field in a
record. For instance,
type bar = {mutable lbl : int};;
let x = {lbl = 1} in
begin match x with {lbl = y} -> y <- 2 end;
x
returns the value {lbl = 2}.
3.5 Directives
In addition to the standard #open and #close directives, Caml Light provides
three additional directives.
#infix " id "
Change the lexical status of the identifier id: in the remainder of the
compilation unit, id is recognized as an infix operator, just like +.
The notation prefix id can be used to refer to the identifier id itself.
Expressions of the form expr_1 id expr_2 are parsed as the application
prefix id expr_1 expr_2. The argument to the #infix directive must be
an identifier, that is, a sequence of letters, digits and underscores
starting with a letter; otherwise, the #infix declaration has no effect.
Example:
#infix "union";;
let prefix union = fun x y -> ... ;;
[1,2] union [3,4];;
#uninfix " id "
Remove the infix status attached to the identifier id by a previous
#infix " id " directive.
#directory " dir-name "
Add the named directory to the path of directories searched for compiled
module interface files. This is equivalent to the -I command-line option
to the batch compiler and the toplevel system.
Part III
The Caml Light library
39
Chapter 4
The core library
This chapter describes the functions provided by the Caml Light core library.
This library is special in two ways:
- It is automatically linked with the user's object code files by the camlc
command (chapter 7). Hence, the globals defined by these libraries can
be used in standalone programs without having to add any .zo file on the
command line for the linking phase. Similarly, in interactive use, these
globals can be used in toplevel phrases without having to load any .zo
file in memory.
- The interfaces for the modules below are automatically ``opened'' when a
compilation starts, or when the toplevel system is launched. Hence, it
is possible to use unqualified identifiers to refer to the functions
provided by these modules, without adding #open directives. Actually,
the list of automatically opened modules depend on the -O option given to
the compiler or to the toplevel system:
--------------------------------------------------------------
|-O option |Opened modules (reverse opening |
| |order) |
--------------------------------------------------------------
|-O cautious (default) |io, eq, int, float, ref, pair, |
| |list, vect, char, string, bool, exc, |
| |stream |
|-O fast |io, eq, int, float, ref, pair, list, |
| |fvect, fchar, fstring, bool, exc, |
| |stream |
|-O none |none |
--------------------------------------------------------------
Conventions
For easy reference, the modules are listed below in alphabetical order of
module names. For each module, the declarations from its interface file are
printed one by one in typewriter font, followed by a short comment. All
modules and the identifiers they export are indexed at the end of this report.
4.1 bool: boolean operations
The boolean and is written e1 & e2. The boolean or is written e1 or e2.
Both constructs are sequential, left-to-right: e2 is evaluated only if
needed. Actually, e1 & e2 is equivalent to if e1 then e2 else false, and
e1 or e2 is equivalent to if e1 then true else e2.
40
Chapter 4. The core library 41
value prefix not : bool -> bool
The boolean negation.
4.2 builtin: base types and constructors
This module defines some types and exceptions for which the language
provides special syntax, and therefore wich are treated specially by the
compiler.
type int
type float
type string
type char
The types of integers, floating-point numbers, character strings, and
characters, respectively.
type exn
The type of exception values.
type bool = false | true
The type of boolean values.
type 'a vect
The type of arrays whose elements have type 'a.
type unit = ()
The type of the unit value.
type 'a list = [] | prefix :: of 'a * 'a list
The type of lists.
exception Match_failure of string * int * int
The exception raised when a pattern-matching fails. The argument
indicates the position in the source code of the pattern-matching (source
file name, position of the first character of the matching, position of
the last character.
4.3 char: character operations
value int_of_char : char -> int
Return the ASCII code of the argument.
value char_of_int : int -> char
Chapter 4. The core library 42
Return the character with the given ASCII code. Raise
Invalid_argument "char_of_int" if the argument is outside the range
0--255.
value char_for_read : char -> string
Return a string representing the given character, with special characters
escaped following the lexical conventions of Caml Light.
4.4 eq: equality functions
value prefix = : 'a -> 'a -> bool
e1 = e2 tests for structural equality of e1 and e2. Mutable structures
(e.g. references) are equal if and only if their current contents are
structurally equal, even if the two mutable objects are not the same
physical object. Equality between functional values raises
Invalid_argument. Equality between cyclic data structures may not
terminate.
value prefix <> : 'a -> 'a -> bool
Negation of prefix =.
value prefix == : 'a -> 'a -> bool
e1 == e2 tests for physical equality of e1 and e2. On integers and
characters, it is the same as structural equality. On mutable
structures, e1 == e2 is true if and only if physical modification of e1
also affects e2. On non-mutable structures, the behavior of prefix == is
implementation-dependent, except that e1 == e2 implies e1 = e2.
value prefix != : 'a -> 'a -> bool
Negation of prefix ==.
4.5 exc: exceptions
value raise : exn -> 'a
Raise the given exception value.
A few general-purpose predefined exceptions.
exception Out_of_memory
Raised by the garbage collector, when there is insufficient memory to
complete the computation.
exception Invalid_argument of string
Raised by some library functions, to signal that the given arguments do
not make sense.
Chapter 4. The core library 43
exception Failure of string
Raised by some library functions, to signal that they are undefined on
the given arguments.
exception Not_found
Raised by search library functions, when the required object could not be
found.
exception Exit
This exception is not raised by any library function. It is provided for
use in your programs.
value failwith : string -> 'a
Raise exception Failure with the given string.
value invalid_arg : string -> 'a
Raise exception Invalid_argument with the given string.
4.6 fchar: character operations, without sanity checks
This module implements the same functions as the char module, but does
not perform bound checks on the arguments of the functions. The
functions are therefore faster than those in the char module, but calling
these functions with incorrect parameters (that is, parameters that would
cause the Invalid_argument exception to be raised by the corresponding
functions in the char module) can crash the program.
4.7 float: operations on floating-point numbers
value int_of_float : float -> int
Truncate the given float to an integer value. The result is unspecified
if it falls outside the range of representable integers.
value float_of_int : int -> float
Convert an integer to floating-point.
value minus : float -> float
value minus_float : float -> float
Unary negation.
value prefix + : float -> float -> float
value prefix +. : float -> float -> float
value add_float : float -> float -> float
Addition.
Chapter 4. The core library 44
value prefix - : float -> float -> float
value prefix -. : float -> float -> float
value sub_float : float -> float -> float
Subtraction.
value prefix * : float -> float -> float
value prefix *. : float -> float -> float
value mult_float : float -> float -> float
Product.
value prefix / : float -> float -> float
value prefix /. : float -> float -> float
value div_float : float -> float -> float
Division. The result is unpredictable if the dividend is 0.0.
value eq_float : float -> float -> bool
value prefix =. : float -> float -> bool
Floating-point equality. Equivalent to generic equality, just faster.
value neq_float : float -> float -> bool
value prefix <>. : float -> float -> bool
Negation of eq_float.
value prefix < : float -> float -> bool
value prefix <. : float -> float -> bool
value lt_float : float -> float -> bool
value prefix > : float -> float -> bool
value prefix >. : float -> float -> bool
value gt_float : float -> float -> bool
value prefix <= : float -> float -> bool
value prefix <=. : float -> float -> bool
value le_float : float -> float -> bool
value prefix >= : float -> float -> bool
value prefix >=. : float -> float -> bool
value ge_float : float -> float -> bool
Usual comparisons between floating-point numbers.
value exp : float -> float
value log : float -> float
value sqrt : float -> float
value power : float -> float -> float
value sin : float -> float
value cos : float -> float
value tan : float -> float
value asin : float -> float
value acos : float -> float
value atan : float -> float
value atan2 : float -> float -> float
Usual transcendental functions on floating-point numbers.
Chapter 4. The core library 45
value abs_float : float -> float
Return the absolute value of the argument.
value string_of_float : float -> string
Convert the given float to its decimal representation.
value float_of_string : string -> float
Convert the given string to a float, in decimal. The result is
unspecified if the given string is not a valid representation of a float.
4.8 fstring: string operations, without sanity checks
This module implements the same functions as the string module, but does
not perform bound checks on the arguments of the functions. The
functions are therefore faster than those in the string module, but
calling these functions with incorrect parameters (that is, parameters
that would cause the Invalid_argument exception to be raised by the
corresponding functions in the string module) can crash the program.
4.9 fvect: operations on vectors, without sanity checks
This module implements the same functions as the vect module, but does
not perform bound checks on the arguments of the functions. The
functions are therefore faster than those in the vect module, but calling
these functions with incorrect parameters (that is, parameters that would
cause the Invalid_argument exception to be raised by the corresponding
functions in the vect module) can crash the program.
4.10 int: operations on integers
31
Integers are 31 bits wide. All operations are taken modulo 2 . They do
not fail on overflow.
exception Division_by_zero
value minus : int -> int
value minus_int : int -> int
Unary negation. You can write -e instead of minus e.
value succ : int -> int
succ x is x+1.
value pred : int -> int
pred x is x-1.
value prefix + : int -> int -> int
value add_int : int -> int -> int
Chapter 4. The core library 46
Addition.
value prefix - : int -> int -> int
value sub_int : int -> int -> int
Subtraction.
value prefix * : int -> int -> int
value mult_int : int -> int -> int
Multiplication.
value prefix / : int -> int -> int
value div_int : int -> int -> int
value prefix quo : int -> int -> int
Integer division. Raise Division_by_zero if the second argument is 0.
Give unpredictable results if either argument is negative.
value prefix mod : int -> int -> int
Remainder. Raise Division_by_zero if the second argument is 0. Give
unpredictable results if either argument is negative.
value eq_int : int -> int -> bool
Integer equality. Equivalent to generic equality, just faster.
value neq_int : int -> int -> bool
Negation of eq_int.
value prefix < : int -> int -> bool
value lt_int : int -> int -> bool
value prefix > : int -> int -> bool
value gt_int : int -> int -> bool
value prefix <= : int -> int -> bool
value le_int : int -> int -> bool
value prefix >= : int -> int -> bool
value ge_int : int -> int -> bool
Usual comparisons between integers.
value min : int -> int -> int
Return the smaller of the arguments.
value max : int -> int -> int
Return the greater of the arguments.
value abs : int -> int
Return the absolute value of the argument.
Chapter 4. The core library 47
Bitwise operations
value prefix land : int -> int -> int
Bitwise logical and.
value prefix lor : int -> int -> int
Bitwise logical or.
value prefix lxor : int -> int -> int
Bitwise logical exclusive or.
value lnot : int -> int
Bitwise complement
value prefix lsl : int -> int -> int
value lshift_left : int -> int -> int
n lsl m, or equivalently lshift_left n m, shifts n to the left by m bits.
value prefix lsr : int -> int -> int
n lsr m shifts n to the right by m bits. This is a logical shift:
zeroes are inserted regardless of sign.
value prefix asr : int -> int -> int
value lshift_right : int -> int -> int
n asr m, or equivalently lshift_right n m, shifts n to the right by m
bits. This is an arithmetic shift: the sign bit is replicated.
Conversion functions
value string_of_int : int -> string
Convert the given integer to its decimal representation.
value int_of_string : string -> int
Convert the given string to an integer, in decimal (by default) or in
hexadecimal, octal or binary if the string begins with 0x, 0o or 0b.
Raise Failure "int_of_string" if the given string is not a valid
representation of an integer.
4.11 io: buffered input and output
type in_channel
type out_channel
The abstract types of input channels and output channels.
Chapter 4. The core library 48
exception End_of_file
Raised when an operation cannot complete, because the end of the file has
been reached.
value stdin : in_channel
value std_in : in_channel
value stdout : out_channel
value std_out : out_channel
value stderr : out_channel
value std_err : out_channel
The standard input, standard output, and standard error output for the
process. std_in, std_out and std_err are respectively synonymous with
stdin, stdout and stderr.
value exit : int -> 'a
Flush all pending writes on std_out and std_err, and terminate the
process, returning the given status code to the operating system (usually
0 to indicate no errors, and a small positive integer to indicate
failure.) This function should be called at the end of all standalone
programs that output results on std_out or std_err; otherwise, the
program may appear to produce no output, or its output may be truncated.
Output functions on standard output
value print_char : char -> unit
Print the character on standard output.
value print_string : string -> unit
Print the string on standard output.
value print_int : int -> unit
Print the integer, in decimal, on standard output.
value print_float : float -> unit
Print the floating-point number, in decimal, on standard output.
value print_endline : string -> unit
Print the string, followed by a newline character, on standard output.
value print_newline : unit -> unit
Print a newline character on standard output, and flush standard output.
This can be used to simulate line buffering of standard output.
Output functions on standard error
value prerr_char : char -> unit
Chapter 4. The core library 49
Print the character on standard error.
value prerr_string : string -> unit
Print the string on standard error.
value prerr_int : int -> unit
Print the integer, in decimal, on standard error.
value prerr_float : float -> unit
Print the floating-point number, in decimal, on standard error.
value prerr_endline : string -> unit
Print the string, followed by a newline character on standard error and
flush standard error.
Input functions on standard input
value read_line : unit -> string
Flush standard output, then read characters from standard input until a
newline character is encountered. Return the string of all characters
read, without the newline character at the end.
value read_int : unit -> int
Flush standard output, then read one line from standard input and convert
it to an integer. Raise Failure "int_of_string" if the line read is not
a valid representation of an integer.
value read_float : unit -> float
Flush standard output, then read one line from standard input and convert
it to a floating-point number. The result is unspecified if the line
read is not a valid representation of a floating-point number.
General output functions
value open_out : string -> out_channel
Open the named file for writing, and return a new output channel on that
file, positionned at the beginning of the file. The file is truncated to
zero length if it already exists. It is created if it does not already
exists. Raise sys__Sys_error if the file could not be opened.
value open_out_bin : string -> out_channel
Same as open_out, but the file is opened in binary mode, so that no
translation takes place during writes. On operating systems that do not
distinguish between text mode and binary mode, this function behaves like
open_out.
Chapter 4. The core library 50
value open_out_gen : sys__open_flag list -> int -> string -> out_channel
open_out_gen mode rights filename opens the file named filename for
writing, as above. The extra argument mode specify the opening mode (see
sys__open). The extra argument rights specifies the file permissions, in
case the file must be created (see sys__open). open_out and open_out_bin
are special cases of this function.
value open_descriptor_out : int -> out_channel
open_descriptor_out fd returns a buffered output channel writing to the
file descriptor fd. The file descriptor fd must have been previously
opened for writing, else the behavior is undefined.
value flush : out_channel -> unit
Flush the buffer associated with the given output channel, performing all
pending writes on that channel. Interactive programs must be careful
about flushing std_out at the right times.
value output_char : out_channel -> char -> unit
Write the character on the given output channel.
value output_string : out_channel -> string -> unit
Write the string on the given output channel.
value output : out_channel -> string -> int -> int -> unit
output chan buff ofs len writes len characters from string buff, starting
at offset ofs, to the output channel chan. Raise
Invalid_argument "output" if ofs and len do not designate a valid
substring of buff.
value output_byte : out_channel -> int -> unit
Write one 8-bit integer (as the single character with that code) on the
given output channel. The given integer is taken modulo 256.
value output_binary_int : out_channel -> int -> unit
Write one integer in binary format on the given output channel. The only
reliable way to read it back is through the input_binary_int function.
The format is compatible across all machines for a given version of Caml
Light.
value output_value : out_channel -> 'a -> unit
Write the representation of a structured value of any type to a channel.
Circularities and sharing inside the value are detected and preserved.
The object can be read back, by the function input_value. The format is
compatible across all machines for a given version of Caml Light.
value seek_out : out_channel -> int -> unit
Chapter 4. The core library 51
seek_out chan pos sets the current writing position to pos for channel
chan. This works only for regular files. On files of other kinds (such
as terminals, pipes and sockets,) the behavior is unspecified.
value pos_out : out_channel -> int
Return the current writing position for the given channel.
value out_channel_length : out_channel -> int
Return the total length (number of characters) of the given channel.
value close_out : out_channel -> unit
Close the given channel, flushing all buffered write operations. The
behavior is unspecified if any of the above functions is called on a
closed channel.
General input functions
value open_in : string -> in_channel
Open the named file for reading, and return a new input channel on that
file, positionned at the beginning of the file. Raise sys__Sys_error if
the file could not be opened.
value open_in_bin : string -> in_channel
Same as open_in, but the file is opened in binary mode, so that no
translation takes place during reads. On operating systems that do not
distinguish between text mode and binary mode, this function behaves like
open_in.
value open_in_gen : sys__open_flag list -> int -> string -> in_channel
open_in_gen mode rights filename opens the file named filename for
reading, as above. The extra arguments mode and rights specify the
opening mode and file permissions (see sys__open). open_in and
open_in_bin are special cases of this function.
value open_descriptor_in : int -> in_channel
open_descriptor_in fd returns a buffered input channel reading from the
file descriptor fd. The file descriptor fd must have been previously
opened for reading, else the behavior is undefined.
value input_char : in_channel -> char
Read one character from the given input channel. Raise End_of_file if
there are no more characters to read.
value input_line : in_channel -> string
Read characters from the given input channel, until a newline character
is encountered. Return the string of all characters read, without the
newline character at the end. Raise End_of_file if the end of the file
is reached before the line is complete.
Chapter 4. The core library 52
value input : in_channel -> string -> int -> int -> int
input chan buff ofs len attempts to read len characters from channel
chan, storing them in string buff, starting at character number ofs. It
returns the actual number of characters read, between 0 and len
(inclusive). A return value of 0 means that the end of file was reached.
A return value between 0 and len exclusive means that no more characters
were available at that time; input must be called again to read the
remaining characters, if desired. Exception Invalid_argument "input" is
raised if ofs and len do not designate a valid substring of buff.
value really_input : in_channel -> string -> int -> int -> unit
input chan buff ofs len reads len characters from channel chan, storing
them in string buff, starting at character number ofs. Raise End_of_file
if the end of file is reached before len characters have been read.
Raise Invalid_argument "really_input" if ofs and len do not designate a
valid substring of buff.
value input_byte : in_channel -> int
Same as input_char, but return the 8-bit integer representing the
character. Raise End_of_file if an end of file was reached.
value input_binary_int : in_channel -> int
Read an integer encoded in binary format from the given input channel.
See output_binary_int. Raise End_of_file if an end of file was reached
while reading the integer.
value input_value : in_channel -> 'a
Read the representation of a structured value, as produced by
output_value, and return the corresponding value. This is not type-safe.
The type of the returned object is not 'a properly speaking: the
returned object has one unique type, which cannot be determined at
compile-time. The programmer should explicitly give the expected type of
the returned value, using the following syntax:
(input_value chan : type). The behavior is unspecified if the object in
the file does not belong to the given type.
value seek_in : in_channel -> int -> unit
seek_in chan pos sets the current reading position to pos for channel
chan.
value pos_in : in_channel -> int
Return the current reading position for the given channel.
value in_channel_length : in_channel -> int
Return the total length (number of characters) of the given channel.
This works only for regular files. On files of other kinds, the result
is meaningless.
Chapter 4. The core library 53
value close_in : in_channel -> unit
Close the given channel. Anything can happen if any of the above
functions is called on a closed channel.
4.12 list: operations on lists
value list_length : 'a list -> int
Return the length (number of elements) of the given list.
value prefix @ : 'a list -> 'a list -> 'a list
List concatenation.
value hd : 'a list -> 'a
Return the first element of the given list. Raise Failure "hd" if the
list is empty.
value tl : 'a list -> 'a list
Return the given list without its first element. Raise Failure "tl" if
the list is empty.
value rev : 'a list -> 'a list
List reversal.
value map : ('a -> 'b) -> 'a list -> 'b list
map f [a1; ...; an] applies function f to a1, ..., an, and builds the
list [f a1; ...; f an] with the results returned by f.
value do_list : ('a -> 'b) -> 'a list -> unit
do_list f [a1; ...; an] applies function f in turn to a1; ...; an,
discarding all the results. It is equivalent to
begin f a1; f a2; ...; f an; () end.
value it_list : ('a -> 'b -> 'a) -> 'a -> 'b list -> 'a
it_list f a [b1; ...; bn] is f (... (f (f a b1) b2) ...) bn.
value list_it : ('a -> 'b -> 'b) -> 'a list -> 'b -> 'b
list_it f [a1; ...; an] b is f a1 (f a2 (... (f an b) ...)).
value map2 : ('a -> 'b -> 'c) -> 'a list -> 'b list -> 'c list
map2 f [a1; ...; an] [b1; ...; bn] is [f a1 b1; ...; f an bn]. Raise
Invalid_argument "map2" if the two lists have different lengths.
value do_list2 : ('a -> 'b -> 'c) -> 'a list -> 'b list -> unit
Chapter 4. The core library 54
do_list2 f [a1; ...; an] [b1; ...; bn] calls in turn
f a1 b1; ...; f an bn, discarding the results. Raise
Invalid_argument "do_list2" if the two lists have different lengths.
value it_list2 : ('a -> 'b -> 'c -> 'a) -> 'a -> 'b list -> 'c list -> 'a
it_list2 f a [b1; ...; bn] [c1; ...; cn] is
f (... (f (f a b1 c1) b2 c2) ...) bn cn. Raise
Invalid_argument "it_list2" if the two lists have different lengths.
value list_it2 : ('a -> 'b -> 'c -> 'c) -> 'a list -> 'b list -> 'c -> 'c
list_it2 f [a1; ...; an] [b1; ...; bn] c is
f a1 b1 (f a2 b2 (... (f an bn c) ...)). Raise
Invalid_argument "list_it2" if the two lists have different lengths.
value flat_map : ('a -> 'b list) -> 'a list -> 'b list
flat_map f [l1; ...; ln] is (f l1) @ (f l2) @ ... @ (f ln).
value for_all : ('a -> bool) -> 'a list -> bool
for_all p [a1; ...; an] is (p a1) & (p a2) & ... & (p an).
value exists : ('a -> bool) -> 'a list -> bool
exists p [a1; ...; an] is (p a1) or (p a2) or ... or (p an).
value mem : 'a -> 'a list -> bool
mem a l is true if and only if a is structurally equal (see module eq) to
an element of l.
value memq : 'a -> 'a list -> bool
memq a l is true if and only if a is physically equal (see module eq) to
an element of l.
value except : 'a -> 'a list -> 'a list
except a l returns the list l where the first element structurally equal
to a has been removed. The list l is returned unchanged if it does not
contain a.
value exceptq : 'a -> 'a list -> 'a list
Same as except, with physical equality instead of structural equality.
value subtract : 'a list -> 'a list -> 'a list
subtract l1 l2 returns the list l1 where all elements structurally equal
to one of the elements of l2 have been removed.
value union : 'a list -> 'a list -> 'a list
union l1 l2 appends before list l2 all the elements of list l1 that are
not structurally equal to an element of l2.
Chapter 4. The core library 55
value intersect : 'a list -> 'a list -> 'a list
intersect l1 l2 returns the list of the elements of l1 that are
structurally equal to an element of l2.
value index : 'a -> 'a list -> int
index a l returns the position of the first element of list l that is
structurally equal to a. The head of the list has position 0. Raise
Not_found if a is not present in l.
value assoc : 'a -> ('a * 'b) list -> 'b
assoc a l returns the value associated with key a in the list of pairs l.
That is, assoc a [ ...; (a,b); ...] = b if (a,b) is the leftmost binding
of a in list l. Raise Not_found if there is no value associated with a
in the list l.
value assq : 'a -> ('a * 'b) list -> 'b
Same as assoc, but use physical equality instead of structural equality
to compare keys.
value mem_assoc : 'a -> ('a * 'b) list -> bool
Same as assoc, but simply return true if a binding exists, and false if
no bindings exist for the given key.
4.13 pair: operations on pairs
value fst : 'a * 'b -> 'a
Return the first component of a pair.
value snd : 'a * 'b -> 'b
Return the second component of a pair.
value split : ('a * 'b) list -> 'a list * 'b list
Transform a list of pairs into a pair of lists:
split [(a1,b1); ...; (an,bn)] is ([a1; ...; an], [b1; ...; bn])
value combine : 'a list * 'b list -> ('a * 'b) list
Transform a pair of lists into a list of pairs:
combine ([a1; ...; an], [b1; ...; bn]) is [(a1,b1); ...; (an,bn)]. Raise
Invalid_argument "combine" if the two lists have different lengths.
value map_combine : ('a * 'b -> 'c) -> 'a list * 'b list -> 'c list
map_combine f ([a1; ...; an], [b1; ...; bn]) is
[f (a1, b1); ...; f (an, bn)]. Raise invalid_argument "map_combine" if
the two lists have different lengths.
Chapter 4. The core library 56
value do_list_combine : ('a * 'b -> 'c) -> 'a list * 'b list -> unit
do_list_combine f ([a1; ...; an], [b1; ...; bn]) calls in turn
f (a1, b1); ...; f (an, bn), discarding the results. Raise
Invalid_argument "do_list_combine" if the two lists have different
lengths.
4.14 ref: operations on references
type 'a ref = ref of mutable 'a
value prefix ! : 'a ref -> 'a
!r returns the current contents of reference r. Could be defined as
fun (ref x) -> x.
value prefix := : 'a ref -> 'a -> unit
r := a stores the value of a in reference r.
value incr : int ref -> unit
Increment the integer contained in the given reference. Could be defined
as fun r -> r := succ !r.
value decr : int ref -> unit
Decrement the integer contained in the given reference. Could be defined
as fun r -> r := pred !r.
4.15 stream: operations on streams
type 'a stream
exception Parse_failure
Raised by parsers when none of the first component of the stream patterns
is accepted
exception Parse_error
Raised by parsers when the first component of a stream pattern is
accepted, but one of the following components is rejected
value stream_next : 'a stream -> 'a
stream_next s returns the first element of stream s, and removes it from
the stream. Raise Parse_failure if the stream is empty.
value stream_from : (unit -> 'a) -> 'a stream
stream_from f returns the stream which fetches its terminals using the
function f. This function could be defined as:
let rec stream_from f = [< 'f(); stream_from f >]
but is implemented more efficiently.
Chapter 4. The core library 57
value stream_of_string : string -> char stream
stream_of_string s returns the stream of the characters in string s.
value stream_of_channel : in_channel -> char stream
stream_of_channel ic returns the stream of characters read on channel ic.
value do_stream : ('a -> 'b) -> 'a stream -> unit
do_stream f s scans the whole stream s, applying the function f in turn
to each terminal encountered
value stream_check : ('a -> bool) -> 'a stream -> 'a
stream_check p returns the parser which returns the first terminal of the
stream if the predicate p returns true on this terminal, and raises
Parse_failure otherwise.
value end_of_stream : 'a stream -> unit
Return () iff the stream is empty, and raise Parse_failure otherwise.
value stream_get : 'a stream -> 'a * 'a stream
stream_get s return the first element of the stream s, and a stream
containing the remaining elements of s. Raise Parse_failure if the
stream is empty. The stream s is not modified. This function makes it
possible to access a stream non-destructively.
4.16 string: string operations
value string_length : string -> int
Return the length (number of characters) of the given string.
value nth_char : string -> int -> char
nth_char s n returns character number n in string s. The first character
is character number 0. The last character is character number
string_length s - 1. Raise Invalid_argument "nth_char" if n is ouside
the range 0 -- (string_length s - 1).
value set_nth_char : string -> int -> char -> unit
set_nth_char s n c modifies string s in place, replacing the character
number n by c. Raise Invalid_argument "set_nth_char" if n is ouside the
range 0 to (string_length s - 1).
value prefix ^ : string -> string -> string
s1 ^ s2 returns a fresh string containing the concatenation of the
strings s1 and s2.
Chapter 4. The core library 58
value sub_string : string -> int -> int -> string
sub_string s start len returns a fresh string of length len, containing
the characters number start to start + len - 1 of string s. Raise
Invalid_argument "sub_string" if start and len do not designate a valid
substring of s; that is, if start < 0, or len < 0, or
start + len > string_length s.
value create_string : int -> string
create_string n returns a fresh string of length n. The string initially
contains arbitrary characters.
value make_string : int -> char -> string
make_string n c returns a fresh string of length n, filled with the
character c.
value fill_string : string -> int -> int -> char -> unit
fill_string s start len c modifies string s in place, replacing the
characters number start to start + len - 1 by c. Raise
Invalid_argument "fill_string" if start and len do not designate a valid
substring of s.
value blit_string : string -> int -> string -> int -> int -> unit
blit_string s1 o1 s2 o2 len copies len characters from string s1,
starting at character number o1, to string s2, starting at character
number o2. It works correctly even if s1 and s2 are the same string, and
the source and destination chunks overlap. Raise
Invalid_argument "blit_string" if o1 and len do not designate a valid
substring of s1, or if o2 and len do not designate a valid substring of
s2.
value replace_string : string -> string -> int -> unit
replace_string dest src start copies all characters from the string src
into the string dst, starting at character number start in dst. Raise
Invalid_argument "replace_string" if copying would overflow string dest.
value eq_string : string -> string -> bool
value neq_string : string -> string -> bool
value le_string : string -> string -> bool
value lt_string : string -> string -> bool
value ge_string : string -> string -> bool
value gt_string : string -> string -> bool
Comparison functions (lexicographic ordering) between strings.
value compare_strings : string -> string -> int
General comparison between strings. compare_strings s1 s2 returns 0 if
s1 and s2 are equal, or else -2 if s1 is a prefix of s2, or 2 if s2 is a
prefix of s1, or else -1 if s1 is lexicographically before s2, or 1 if s2
is lexicographically before s1.
Chapter 4. The core library 59
value string_for_read : string -> string
Return a copy of the argument, with special characters represented by
escape sequences, following the lexical conventions of Caml Light.
4.17 vect: operations on vectors
value vect_length : 'a vect -> int
Return the length (number of elements) of the given vector.
value vect_item : 'a vect -> int -> 'a
vect_item v n returns the element number n of vector v. The first
element has number 0. The last element has number vect_length v - 1.
Raise Invalid_argument "vect_item" if n is outside the range 0 --
(vect_length v - 1). You can also write v.(n) instead of vect_item v n.
value vect_assign : 'a vect -> int -> 'a -> unit
vect_assign v n x modifies vector v in place, replacing element number n
with x. Raise Invalid_argument "vect_assign" if n is outside the range 0
-- vect_length v - 1. You can also write v.(n) <- x instead of
vect_assign v n x.
value make_vect : int -> 'a -> 'a vect
make_vect n x returns a fresh vector of length n, initialized with x.
All the elements of this new vector are initially eq to x.
value make_matrix : int -> int -> 'a -> 'a vect vect
make_matrix dimx dimy e returns a two-dimensional array (a vector of
vectors) with first dimension dimx and second dimension dimy. All the
elements of this new matrix are initially eq to e. The element (x,y) of
a matrix m is accessed with the notation m.(x).(y).
value concat_vect : 'a vect -> 'a vect -> 'a vect
concat_vect v1 v2 returns a fresh vector containing the concatenation of
vectors v1 and v2.
value sub_vect : 'a vect -> int -> int -> 'a vect
sub_vect v start len returns a fresh vector of length len, containing the
elements number start to start + len - 1 of vector v. Raise
Invalid_argument "sub_vect" if start and len do not designate a valid
subvector of v; that is, if start < 0, or len < 0, or
start + len > vect_length v.
value copy_vect : 'a vect -> 'a vect
copy_vect v returns a copy of v, that is, a fresh vector containing the
same elements as v.
Chapter 4. The core library 60
value fill_vect : 'a vect -> int -> int -> 'a -> unit
fill_vect v ofs len x modifies vector v in place, storing x in elements
number ofs to ofs + len - 1. Raise Invalid_argument "fill_vect" if ofs
and len do not designate a valid subvector of v.
value blit_vect : 'a vect -> int -> 'a vect -> int -> int -> unit
blit_vect v1 o1 v2 o2 len copies len elements from vector v1, starting at
element number o1, to vector v2, starting at element number o2. It works
correctly even if v1 and v2 are the same vector, and the source and
destination chunks overlap. Raise Invalid_argument "blit_vect" if o1 and
len do not designate a valid subvector of v1, or if o2 and len do not
designate a valid subvector of v2.
value list_of_vect : 'a vect -> 'a list
list_of_vect v returns the list of all the elements of v, that is:
[v.(0); v.(1); ...; v.(vect_length v - 1)].
value vect_of_list : 'a list -> 'a vect
vect_of_list l returns a fresh vector containing the elements of l.
value map_vect : ('a -> 'b) -> 'a vect -> 'b vect
map_vect f v applies function f to all the elements of v, and builds a
vector with the results returned by f:
[| f v.(0); f v.(1); ...; f v.(vect_length v - 1) |].
value map_vect_list : ('a -> 'b) -> 'a vect -> 'b list
map_vect_list f v applies function f to all the elements of v, and builds
a list with the results returned by f:
[ f v.(0); f v.(1); ...; f v.(vect_length v - 1) ].
value do_vect : ('a -> 'b) -> 'a vect -> unit
do_vect f v applies function f in turn to all the elements of v,
discarding all the results:
f v.(0); f v.(1); ...; f v.(vect_length v - 1); ().
Chapter 5
The standard library
This chapter describes the functions provided by the Caml Light standard
library. Just as the modules from the core library, the modules from the
standard library are automatically linked with the user's object code files by
the camlc command. Hence, the globals defined by these libraries can be used
in standalone programs without having to add any .zo file on the command line
for the linking phase. Similarly, in interactive use, these globals can be
used in toplevel phrases without having to load any .zo file in memory.
Unlike the modules from the core library, the modules from the standard
library are not automatically ``opened'' when a compilation starts, or when
the toplevel system is launched. Hence it is necessary to use qualified
identifiers to refer to the functions provided by these modules, or to add
#open directives.
Conventions
For easy reference, the modules are listed below in alphabetical order of
module names. For each module, the declarations from its interface file are
printed one by one in typewriter font, followed by a short comment. All
modules and the identifiers they export are indexed at the end of this report.
5.1 arg: parsing of command line arguments
This module provides a general mechanism for extracting options and
arguments from the command line to the program.
Syntax of command lines. A keyword is a character string starting with a
-. An option is a keyword alone or followed by an argument. There are 4
types of keywords: Unit, String, Int, and Float. Unit keywords do not
take an argument. String, Int, and Float keywords take the following
word on the command line as an argument. Arguments not preceded by a
keyword are called anonymous arguments. Examples (foo is assumed to be
the command name):
foo -flag (a unit option)
foo -int 1 (an int option with argument 1)
foo -string foobar (a string option with argument "foobar")
foo -float 12.34 (a float option with argument 12.34)
foo 1 2 3 (three anonymous arguments: "1", "2", and "3")
foo 1 2 -flag 3 -string bar 4
(four anonymous arguments, a unit option, and
a string option with argument "bar")
61
Chapter 5. The standard library 62
type spec =
String of (string -> unit)
| Int of (int -> unit)
| Unit of (unit -> unit)
| Float of (float -> unit)
The concrete type describing the behavior associated with a keyword.
value parse : (string * spec) list -> (string -> unit) -> unit
parse speclist anonfun parses the command line, calling the functions in
speclist whenever appropriate, and anonfun on anonymous arguments. The
functions are called in the same order as they appear on the command
line. The strings in the (string * spec) list are keywords and must
start with a -, else they are ignored. For the user to be able to
specify anonymous arguments starting with a -, include for example
("--", String anonfun) in speclist.
exception Bad of string
Functions in speclist or anonfun can raise Bad message to reject invalid
arguments.
5.2 baltree: basic balanced binary trees
This module implements balanced ordered binary trees. All operations
over binary trees are applicative (no side-effects). The set and map
modules are based on this module. This modules gives a more direct
access to the internals of the binary tree implementation than the set
and map abstractions, but is more delicate to use and not as safe. For
advanced users only.
type 'a t = Empty | Node of 'a t * 'a * 'a t * int
The type of trees containing elements of type 'a. Empty is the empty
tree (containing no elements).
type 'a contents = Nothing | Something of 'a
Used with the functions modify and split, to represent the presence or
the absence of an element in a tree.
value add: ('a -> int) -> 'a -> 'a t -> 'a t
add f x t inserts the element x into the tree t. f is an ordering
function: f y must return 0 if x and y are equal (or equivalent), a
negative integer if x is smaller than y, and a positive integer if x is
greater than y. The tree t is returned unchanged if it already contains
an element equivalent to x (that is, an element y such that f y is 0).
The ordering f must be consistent with the orderings used to build t with
add, remove, modify or split operations.
value contains: ('a -> int) -> 'a t -> bool
contains f t checks whether t contains an element satisfying f, that is,
an element x such that f x is 0. f is an ordering function with the same
Chapter 5. The standard library 63
constraints as for add. It can be coarser (identify more elements) than
the orderings used to build t, but must be consistent with them.
value find: ('a -> int) -> 'a t -> 'a
Same as contains, except that find f t returns the element x such that
f x is 0, or raises Not_found if none has been found.
value remove: ('a -> int) -> 'a t -> 'a t
remove f t removes one element x of t such that f x is 0. f is an
ordering function with the same constraints as for add. t is returned
unchanged if it does not contain any element satisfying f. If several
elements of t satisfy f, only one is removed.
value modify: ('a -> int) -> ('a contents -> 'a contents) -> 'a t -> 'a t
General insertion/modification/deletion function. modify f g t searchs t
for an element x satisfying the ordering function f. If one is found, g
is applied to Something x; if g returns Nothing, the element x is
removed; if g returns Something y, the element y replaces x in the tree.
(It is assumed that x and y are equivalent, in particular, that f y is
0.) If the tree does not contain any x satisfying f, g is applied to
Nothing; if it returns Nothing, the tree is returned unchanged; if it
returns Something x, the element x is inserted in the tree. (It is
assumed that f x is 0.) The functions add and remove are special cases
of modify, slightly more efficient.
value split: ('a -> int) -> 'a t -> 'a t * 'a contents * 'a t
split f t returns a triple (less, elt, greater) where less is a tree
containing all elements x of t such that f x is negative, greater is a
tree containing all elements x of t such that f x is positive, and elt is
Something x if t contains an element x such that f x is 0, and Nothing
otherwise.
value compare: ('a -> 'a -> int) -> 'a t -> 'a t -> int
Compare two trees. The first argument f is a comparison function over
the tree elements: f e1 e2 is zero if the elements e1 and e2 are equal,
negative if e1 is smaller than e2, and positive if e1 is greater than e2.
compare f t1 t2 compares the fringes of t1 and t2 by lexicographic
extension of f.
5.3 filename: operations on file names
value current_dir_name : string
The conventional name for the current directory (e.g. . in Unix).
value concat : string -> string -> string
concat dir file returns a file name that designates file file in
directory dir.
Chapter 5. The standard library 64
value is_absolute : string -> bool
Return true if the file name is absolute or starts with an explicit
reference to the current directory (./ or ../ in Unix), and false if it
is relative to the current directory.
value check_suffix : string -> string -> bool
check_suffix name suff returns true if the filename name ends with the
suffix suff.
value chop_suffix : string -> string -> string
chop_suffix name suff removes the suffix suff from the filename name.
The behavior is undefined if name does not end up with the suffix suff.
value basename : string -> string
value dirname : string -> string
Split a file name into directory name / base file name.
concat (dirname name) (basename name) returns a file name which is
equivalent to name. Moreover, after setting the current directory to
dirname name (with sys__chdir), references to basename name (which is a
relative file name) designate the same file as name before the call to
chdir.
5.4 genlex: a generic lexical analyzer
This module implements a simple ``standard'' lexical analyzer, presented
as a function from character streams to token streams. It implements
roughly the lexical conventions of Caml, but is parameterized by the set
of keywords of your language.
type token =
Kwd of string
| Ident of string
| Int of int
| Float of float
| String of string
| Char of char
The type of tokens. The lexical classes are: Int and Float for integer
and floating-point numbers; String for string literals, enclosed in
double quotes; Char for character literals, enclosed in backquotes; Ident
for identifiers (either sequences of letters, digits, underscores and
quotes, or sequences of ``operator characters'' such as +, *, etc); and
Kwd for keywords (either identifiers or single ``special characters''
such as (, }, etc).
value make_lexer: string list -> (char stream -> token stream)
Construct the lexer function. The first argument is the list of
keywords. An identifier s is returned as Kwd s if s belongs to this
list, and as Ident s otherwise. A special character s is returned as
Kwd s if s belongs to this list, and cause a lexical error (exception
Parse_error) otherwise. Blanks and newlines are skipped. Comments
Chapter 5. The standard library 65
delimited by (* and *) are skipped as well, and can be nested. Example:
a lexer suitable for a desk calculator is obtained by
let lexer = make_lexer ["+";"-";"*";"/";"let";"="; "("; ")"]
The associated parser would be a function from token stream to, for
instance, int, and would have rules such as:
let parse_expr = function
[< 'Int n >] -> n
| [< 'Kwd "("; parse_expr n; 'Kwd ")" >] -> n
| [< parse_expr n1; (parse_end n1) n2 >] -> n2
and parse_end n1 = function
[< 'Kwd "+"; parse_expr n2 >] -> n1+n2
| ...
5.5 hashtbl: hash tables and hash functions
Hash tables are hashed association tables, with in-place modification.
type ('a, 'b) t mutable
The type of hash tables from type 'a to type 'b.
value new : int -> ('a,'b) t
new n creates a new, empty hash table, with initial size n. The table
grows as needed, so n is just an initial guess. Better results are said
to be achieved when n is a prime number.
value clear : ('a, 'b) t -> unit
Empty a hash table.
value add : ('a, 'b) t -> 'a -> 'b -> unit
add tbl x y adds a binding of x to y in table tbl. Previous bindings for
x are not removed, but simply hidden. That is, after performing
remove tbl x, the previous binding for x, if any, is restored. (This is
the semantics of association lists.)
value find : ('a, 'b) t -> 'a -> 'b
find tbl x returns the current binding of x in tbl, or raises Not_found
if no such binding exists.
value find_all : ('a, 'b) t -> 'a -> 'b list
find_all tbl x returns the list of all data associated with x in tbl.
The current binding is returned first, then the previous bindings, in
reverse order of introduction in the table.
Chapter 5. The standard library 66
value remove : ('a, 'b) t -> 'a -> unit
remove tbl x removes the current binding of x in tbl, restoring the
previous binding if it exists. It does nothing if x is not bound in tbl.
value do_table : ('a -> 'b -> 'c) -> ('a, 'b) t -> unit
do_table f tbl applies f to all bindings in table tbl, discarding all the
results. f receives the key as first argument, and the associated value
as second argument. The order in which the bindings are passed to f is
unpredictable. The same binding can be presented several times to f.
The polymorphic hash primitive
value hash : 'a -> int
hash x associates a positive integer to any value of any type. It is
guaranteed that if x = y, then hash x = hash y. Moreover, hash always
terminates, even on cyclic structures.
value hash_param : int -> int -> 'a -> int
hash_param n m x computes a hash value for x, with the same properties as
for hash. The two extra parameters n and m give more precise control
over hashing. Hashing performs a depth-first, right-to-left traversal of
the structure x, stopping after n meaningful nodes were encountered, or m
nodes, meaningful or not, were encountered. Meaningful nodes are:
integers; floating-point numbers; strings; characters; booleans; and
constant constructors. Larger values of m and n means that more nodes
are taken into account to compute the final hash value, and therefore
collisions are less likely to happen. However, hashing takes longer.
The parameters m and n govern the tradeoff between accuracy and speed.
5.6 lexing: the run-time library for lexers generated by camllex
Lexer buffers
type lexbuf =
{ refill_buff : lexbuf -> unit;
lex_buffer : string;
mutable lex_abs_pos : int;
mutable lex_start_pos : int;
mutable lex_curr_pos : int;
mutable lex_last_pos : int;
mutable lex_last_action : lexbuf -> obj }
The type of lexer buffers. A lexer buffer is the argument passed to the
scanning functions defined by the generated scanners. The lexer buffer
holds the current state of the scanner, plus a function to refill the
buffer from the input.
value create_lexer_channel : in_channel -> lexbuf
Create a lexer buffer on the given input channel.
create_lexer_channel inchan returns a lexer buffer which reads from the
Chapter 5. The standard library 67
input channel inchan, at the current reading position.
value create_lexer_string : string -> lexbuf
Create a lexer buffer which reads from the given string. Reading starts
from the first character in the string. An end-of-input condition is
generated when the end of the string is reached.
value create_lexer : (string -> int -> int) -> lexbuf
Create a lexer buffer with the given function as its reading method.
When the scanner needs more characters, it will call the given function,
giving it a character string s and a character count n. The function
should put n characters or less in s, starting at character number 0, and
return the number of characters provided. A return value of 0 means end
of input.
Functions for lexer semantic actions
The following functions can be called from the semantic actions of lexer
definitions (the ML code enclosed in braces that computes the value
returned by lexing functions). They give access to the character string
matched by the regular expression associated with the semantic action.
These functions must be applied to the argument lexbuf, which, in the
code generated by camllex, is bound to the lexer buffer passed to the
parsing function.
value get_lexeme : lexbuf -> string
get_lexeme lexbuf returns the string matched by the regular expression.
value get_lexeme_char : lexbuf -> int -> char
get_lexeme_char lexbuf i returns character number i in the matched
string.
value get_lexeme_start : lexbuf -> int
get_lexeme_start lexbuf returns the position in the input stream of the
first character of the matched string. The first character of the stream
has position 0.
value get_lexeme_end : lexbuf -> int
get_lexeme_start lexbuf returns the position in the input stream of the
character following the last character of the matched string. The first
character of the stream has position 0.
5.7 map: association tables over ordered types
This module implements applicative association tables, also known as
finite maps or dictionaries, given a total ordering function over the
keys. All operations over maps are purely applicative (no side-effects).
The implementation uses balanced binary trees, and therefore searching
and insertion take time logarithmic in the size of the map.
Chapter 5. The standard library 68
type ('a, 'b) t
The type of maps from type 'a to type 'b.
value empty: ('a -> 'a -> int) -> ('a, 'b) t
The empty map. The argument is a total ordering function over the set
elements. This is a two-argument function f such that f e1 e2 is zero if
the elements e1 and e2 are equal, f e1 e2 is strictly negative if e1 is
smaller than e2, and f e1 e2 is strictly positive if e1 is greater than
e2. Examples: a suitable ordering function for type int is prefix -.
For type string, you could use compare_strings.
value add: 'a -> 'b -> ('a, 'b) t -> ('a, 'b) t
add x y m returns a map containing the same bindings as m, plus a binding
of x to y. Previous bindings for x in m are not removed, but simply
hidden: they reappear after performing a remove operation. (This is the
semantics of association lists.)
value find:'a -> ('a, 'b) t -> 'b
find x m returns the current binding of x in m, or raises Not_found if no
such binding exists.
value remove: 'a -> ('a, 'b) t -> ('a, 'b) t
remove x m returns a map containing the same bindings as m except the
current binding for x. The previous binding for x is restored if it
exists. m is returned unchanged if x is not bound in m.
value iter: ('a -> 'b -> 'c) -> ('a, 'b) t -> unit
iter f m applies f to all bindings in map m, discarding the results. f
receives the key as first argument, and the associated value as second
argument. The order in which the bindings are passed to f is
unspecified. Only current bindings are presented to f: bindings hidden
by more recent bindings are not passed to f.
5.8 parsing: the run-time library for parsers generated by mlyacc
The following functions can be called by user code.
value symbol_start : unit -> int
value symbol_end : unit -> int
symbol_start and symbol_end are to be called in the action part of a
grammar rule only. They return the position of the string that matches
the left-hand side of the rule: symbol_start() returns the position of
the first character; symbol_end() returns the position of the last
character, plus one. The first character in a file is at position 0.
value rhs_start: int -> int
value rhs_end: int -> int
Chapter 5. The standard library 69
Same as symbol_start and symbol_end above, but return then position of
the string matching the nth item on the right-hand side of the rule,
where n is the integer parameter to lhs_start and lhs_end. n is 1 for
the leftmost item.
value clear_parser : unit -> unit
Empty the parser stack. Call it just after a parsing function has
returned, to remove all pointers from the parser stack to structures that
were built by semantic actions during parsing. This is optional, but
lowers the memory requirements of the programs.
5.9 printexc: a catch-all exception handler
value f: ('a -> 'b) -> 'a -> 'b
f fn x applies fn to x and returns the result. If the evaluation of fn x
raises any exception, the name of the exception is printed on standard
error output, and the programs aborts with exit code 2. Typical use is
f main (), where main, with type unit->unit, is the entry point of a
standalone program, to catch and print stray exceptions. For f to work
properly, the program must be linked with the -g option.
5.10 printf: formatting printing functions
value fprintf: out_channel -> string -> 'a
fprintf outchan format arg1 ... argN formats the arguments arg1 to argN
according to the format string format, and outputs the resulting string
on the channel outchan. The format is a character string which contains
two types of objects: plain characters, which are simply copied to the
output channel, and conversion specifications, each of which causes
conversion and printing of one argument. Conversion specifications
consist in the % character, followed by optional flags and field widths,
followed by one conversion character. The conversion characters and
their meanings are:
d or i: convert an integer argument to signed decimal
u: convert an integer argument to unsigned decimal
x: convert an integer argument to unsigned hexadecimal, using lowercase
letters.
X: convert an integer argument to unsigned hexadecimal, using uppercase
letters.
s: insert a string argument
c: insert a character argument
f: convert a floating-point argument to decimal notation, in the style
dddd.ddd
e or E: convert a floating-point argument to decimal notation, in the
style d.ddd e+-dd (mantissa and exponent)
g or G: convert a floating-point argument to decimal notation, in style f
or e, E (whichever is more compact)
b: convert a boolean argument to the string true or false
Refer to the C library printf function for the meaning of flags and field
width specifiers. The exception Invalid_argument is raised if the types
of the provided arguments do not match the format. The exception is also
raised if too many arguments are provided. If too few arguments are
Chapter 5. The standard library 70
provided, printing stops just before converting the first missing
argument.
value printf: string -> 'a
Same as fprintf, but output on std_out.
value fprint: out_channel -> string -> unit
Print the given string on the given output channel, without any
formatting.
value print: string -> unit
Print the given string on std_out, without any formatting. This is the
same function as print_string of module io.
5.11 queue: queues
This module implements queues (FIFOs), with in-place modification.
type 'a t mutable
The type of queues containing elements of type 'a.
exception Empty
Raised when take is applied to an empty queue.
value new: unit -> 'a t
Return a new queue, initially empty.
value add: 'a -> 'a t -> unit
add x q adds the element x at the end of the queue q.
value take: 'a t -> 'a
take q removes and returns the first element in queue q, or raises Empty
if the queue is empty.
value peek: 'a t -> 'a
peek q returns the first element in queue q, without removing it from the
queue, or raises Empty if the queue is empty.
value clear : 'a t -> unit
Discard all elements from a queue.
value length: 'a t -> int
Return the number of elements in a queue.
Chapter 5. The standard library 71
value iter: ('a -> 'b) -> 'a t -> unit
iter f q applies f in turn to all elements of q, from the least recently
entered to the most recently entered. The queue itself is unchanged.
5.12 random: pseudo-random number generator
value init : int -> unit
Initialize the generator, using the argument as a seed. The same seed
will always yield the same sequence of numbers.
value int : int -> int
random__int bound returns a random number between 0 (inclusive) and bound
30
(exclusive). bound must be smaller than 2 .
value float : float -> float
random__float returns a random number between 0 (inclusive) and bound
(exclusive).
5.13 set: sets over ordered types
This module implements the set data structure, given a total ordering
function over the set elements. All operations over sets are purely
applicative (no side-effects). The implementation uses balanced binary
trees, and is therefore reasonably efficient: insertion and membership
take time logarithmic in the size of the set, for instance.
type 'a t
The type of sets containing elements of type 'a.
value empty: ('a -> 'a -> int) -> 'a t
The empty set. The argument is a total ordering function over the set
elements. This is a two-argument function f such that f e1 e2 is zero if
the elements e1 and e2 are equal, f e1 e2 is strictly negative if e1 is
smaller than e2, and f e1 e2 is strictly positive if e1 is greater than
e2. Examples: a suitable ordering function for type int is prefix -.
For type string, you could use compare_strings.
value is_empty: 'a t -> bool
Test whether a set is empty or not.
value mem: 'a -> 'a t -> bool
mem x s tests whether x belongs to the set s.
value add: 'a -> 'a t -> 'a t
Chapter 5. The standard library 72
add x s returns a set containing all elements of s, plus x. If x was
already in s, s is returned unchanged.
value remove: 'a -> 'a t -> 'a t
remove x s returns a set containing all elements of s, except x. If x
was not in s, s is returned unchanged.
value union: 'a t -> 'a t -> 'a t
value inter: 'a t -> 'a t -> 'a t
value diff: 'a t -> 'a t -> 'a t
Union, intersection and set difference.
value equal: 'a t -> 'a t -> bool
equal s1 s2 tests whether the sets s1 and s2 are equal, that is, contain
the same elements.
value compare: 'a t -> 'a t -> int
Total ordering between sets. Can be used as the ordering function for
doing sets of sets.
value elements: 'a t -> 'a list
Return the list of all elements of the given set. The elements appear in
the list in some non-specified order.
value iter: ('a -> 'b) -> 'a t -> unit
iter f s applies f in turn to all elements of s, and discards the
results. The elements of s are presented to f in a non-specified order.
value fold: ('a -> 'b -> 'b) -> 'a t -> 'b -> 'b
fold f s a computes (f xN ... (f x2 (f x1 a))...), where x1 ... xN are
the elements of s. The order in which elements of s are presented to f
is not specified.
5.14 sort: sorting and merging lists
value sort : ('a -> 'a -> bool) -> 'a list -> 'a list
Sort a list in increasing order according to an ordering predicate. The
predicate should return true if its first argument is less than or equal
to its second argument.
value merge : ('a -> 'a -> bool) -> 'a list -> 'a list -> 'a list
Merge two lists according to the given predicate. Assuming the two
argument lists are sorted according to the predicate, merge returns a
sorted list containing the elements from the two lists. The behavior is
undefined if the two argument lists were not sorted.
Chapter 5. The standard library 73
5.15 stack: stacks
This module implements stacks (LIFOs), with in-place modification.
type 'a t mutable
The type of stacks containing elements of type 'a.
exception Empty
Raised when pop is applied to an empty stack.
value new: unit -> 'a t
Return a new stack, initially empty.
value push: 'a -> 'a t -> unit
push x s adds the element x at the top of stack s.
value pop: 'a t -> 'a
pop s removes and returns the topmost element in stack s, or raises Empty
if the stack is empty.
value clear : 'a t -> unit
Discard all elements from a stack.
value length: 'a t -> int
Return the number of elements in a stack.
value iter: ('a -> 'b) -> 'a t -> unit
iter f s applies f in turn to all elements of s, from the element at the
top of the stack to the element at the bottom of the stack. The stack
itself is unchanged.
5.16 sys: system interface
This module provides a simple interface to the operating system.
exception Sys_error of string
Raised by some functions in the sys and io modules, when the underlying
system calls fail. The argument to Sys_error is a string describing the
error. The texts of the error messages are implementation-dependent, and
should not be relied upon to catch specific system errors.
value command_line : string vect
The command line arguments given to the process. The first element is
the command name used to invoke the program.
Chapter 5. The standard library 74
value interactive: bool
True if we're running under the toplevel system. False if we're running
as a standalone program.
type file_perm == int
value s_irusr : file_perm
value s_iwusr : file_perm
value s_ixusr : file_perm
value s_irgrp : file_perm
value s_iwgrp : file_perm
value s_ixgrp : file_perm
value s_iroth : file_perm
value s_iwoth : file_perm
value s_ixoth : file_perm
value s_isuid : file_perm
value s_isgid : file_perm
value s_irall : file_perm
value s_iwall : file_perm
value s_ixall : file_perm
Access permissions for files. r is reading permission, w is writing
permission, x is execution permission. usr means permissions for the
user owning the file, grp for the group owning the file, oth for others.
isuid and isgid are for set-user-id and set-group-id files, respectively.
The remaining are combinations of the permissions above.
type open_flag =
O_RDONLY (* open read-only *)
| O_WRONLY (* open write-only *)
| O_RDWR (* open for reading and writing *)
| O_APPEND (* open for appending *)
| O_CREAT (* create the file if nonexistent *)
| O_TRUNC (* truncate the file to 0 if it exists *)
| O_EXCL (* fails if the file exists *)
| O_BINARY (* open in binary mode *)
| O_TEXT (* open in text mode *)
The commands for open.
value exit : int -> 'a
Terminate the program and return the given status code to the operating
system. In contrast with the function exit from module io, this exit
function does not flush the standard output and standard error channels.
value open : string -> open_flag list -> file_perm -> int
Open a file. The second argument is the opening mode. The third
argument is the permissions to use if the file must be created. The
result is a file descriptor opened on the file.
value close : int -> unit
Close a file descriptor.
value remove : string -> unit
Chapter 5. The standard library 75
Remove the given file name from the file system.
value rename : string -> string -> unit
Rename a file. The first argument is the old name and the second is the
new name.
value getenv : string -> string
Return the value associated to a variable in the process environment.
Raise Not_found if the variable is unbound.
value chdir : string -> unit
Change the current working directory of the process. Note that there is
no easy way of getting the current working directory from the operating
system.
exception Break
Exception Break is raised on user interrupt if catch_break is on.
value catch_break : bool -> unit
catch_break governs whether user interrupt terminates the program or
raises the Break exception. Call catch_break true to enable raising
Break, and catch_break false to let the system terminate the program on
user interrupt.
Chapter 6
The graphics library
This chapter describes the portable graphics primitives that come standard in
the implementation of Caml Light on micro-computers.
Unix: On Unix workstations running the X11 windows system, an implementation
of the graphics primitives is available in the directory
contrib/libgraph in the distribution. See the file README in this
directory for information on building and using camlgraph, a toplevel
system that includes the graphics primitives, and linking standalone
programs with the library. Drawing takes place in a separate window
that is created when open_graph is called.
Mac: The graphics primitive are available from the standalone application
that runs the toplevel system. They are not available from programs
compiled by camlc and run under the MPW shell. Drawing takes place in
a separate window, that can be made visible with the ``Show graphics
window'' menu entry.
PC: The graphics primitive are available both at toplevel and in separately
compiled programs. The open_graph primitive switches the whole screen
to graphics mode. Under the toplevel system, the user's phrases and
the system responses are printed on the graphics screen too, possibly
overwriting parts of the drawings, and causing scrolling when the
bottom of the screen is reached.
The screen coordinates are interpreted as shown in the figure below. Notice
that the coordinate system used is the same as in mathematics: y increases
from the bottom of the screen to the top of the screen, and angles are
measured counterclockwisey(in degrees). Drawing is clipped to the screen.
|
-------------------------
size_y() | |
| Screen |
| |
| |
| |pixel at (x,y) |
y ---------
| | |
| | |
| | |
| | |
| |
------------------------------
| | | x
| x size_x()
76
Chapter 6. The graphics library 77
Here are the graphics mode specifications supported by open_graph on the
various implementations of this library.
Unix: The argument to open_graph has the format "display-name geometry",
where display-name is the name of the X-windows display to connect to,
and geometry is a standard X-windows geometry specification. The two
components are separated by a space. Either can be omitted, or both.
Examples:
open_graph "foo:0"
connects to the display foo:0 and creates a window with the default
geometry
open_graph "foo:0 300x100+50-0"
connects to the display foo:0 and creates a window 300 pixels wide
by 100 pixels tall, at location (50,0)
open_graph " 300x100+50-0"
connects to the default display and creates a window 300 pixels
wide by 100 pixels tall, at location (50,0)
open_graph ""
connects to the default display and creates a window with the
default geometry.
Mac: The argument to open_graph is ignored.
86: The 86 PC version supports the CGA, EGA and VGA graphics cards. The
argument to open_graph is interpreted as follows:
-----------------------------------------------------
|Argument to open_graph |Graphic mode |
-----------------------------------------------------
| "cga" |320x200, 4 colors |
| "ega_low" |640x200, 16 colors |
| "ega_high" |640x350, 16 colors |
| "vga_low" |640x200, 16 colors |
| "vga_med" |640x350, 16 colors |
| "vga_high" |640x480, 16 colors |
| anything else |highest possible resolution |
-----------------------------------------------------
386: The 386 PC version supports VGA graphics cards, and a number of
SuperVGA cards, provided the correct driver has been installed. (See
the installation instructions.) Only 256 color modes are supported.
This means a resolution of 320x200 on standard VGA, and from 640x480 to
1024x768 on SuperVGA.
The graphics primitive do not work if Caml Light runs under Windows 3
or any DPMI-compliant memory manager.
The argument to open_graph is interpreted as follows:
Chapter 6. The graphics library 78
---------------------------------------------------------------
|Argument to open_graph |Graphic mode |
---------------------------------------------------------------
| "highest" |highest possible resolution |
| "noninterlaced" |highest possible resolution, non- |
| |interlaced mode |
| "320x200" |standard 320x200 VGA mode |
| "wxh" |at least w by h pixels, if possible |
| anything else |default resolution, as set in the |
| |GO32 variable (see the installation |
| |instructions). |
---------------------------------------------------------------
6.1 graphics: machine-independent graphics primitives
exception Graphic_failure of string
Raised by the functions below when they encounter an error.
Initializations
value open_graph: string -> unit
Show the graphics window or switch the screen to graphic mode. The
graphics window is cleared. The string argument is used to pass optional
information on the desired graphics mode, the graphics window size, and
so on. Its interpretation is implementation-dependent. If the empty
string is given, a sensible default is selected.
value close_graph: unit -> unit
Delete the graphics window or switch the screen back to text mode.
value clear_graph : unit -> unit
Erase the graphics window.
value size_x : unit -> int
value size_y : unit -> int
Return the size of the graphics window. Coordinates of the screen pixels
range over 0 .. size_x()-1 and 0 .. size_y()-1. Drawings outside of this
rectangle are clipped, without causing an error. The origin (0,0) is at
the lower left corner.
Colors
type color == int
A color is specified by its R, G, B components. Each component is in the
range 0..255. The three components are packed in an int: 0xRRGGBB,
where RR are the two hexadecimal digits for the red component, GG for the
green component, BB for the blue component.
value rgb: int -> int -> int -> int
rgb r g b returns the integer encoding the color with red component r,
green component g, and blue component b. r, g and b are in the range
Chapter 6. The graphics library 79
0..255.
value set_color : color -> unit
Set the current drawing color.
value black : color
value white : color
value red : color
value green : color
value blue : color
value yellow : color
value cyan : color
value magenta : color
Some predefined colors.
value background: color
value foreground: color
Default background and foreground colors (usually, either black
foreground on a white background or white foreground on a black
background). clear_graph fills the screen with the background color.
The initial drawing color is foreground.
Point and line drawing
value plot : int -> int -> unit
Plot the given point with the current drawing color.
value point_color : int -> int -> color
Return the color of the given point.
value moveto : int -> int -> unit
Position the current point.
value current_point : unit -> int * int
Return the position of the current point.
value lineto : int -> int -> unit
Draw a line with endpoints the current point and the given point, and
move the current point to the given point.
value draw_arc : int -> int -> int -> int -> int -> int -> unit
draw_arc x y rx ry a1 a2 draws an elliptical arc with center x,y,
horizontal radius rx, vertical radius ry, from angle a1 to angle a2 (in
degrees). The current point is unchanged.
value draw_ellipse : int -> int -> int -> int -> unit
Chapter 6. The graphics library 80
draw_ellipse x y rx ry draws an ellipse with center x,y, horizontal
radius rx and vertical radius ry. The current point is unchanged.
value draw_circle : int -> int -> int -> unit
draw_circle x y r draws a circle with center x,y and radius r. The
current point is unchanged.
value set_line_width : int -> unit
Set the width of points and lines drawn with the functions above.
Text drawing
value draw_char : char -> unit
value draw_string : string -> unit
Draw a character or a character string with lower left corner at current
position. After drawing, the current position is set to the lower right
corner of the text drawn.
value set_font : string -> unit
value set_text_size : int -> unit
Set the font and character size used for drawing text. The
interpretation of the arguments to set_font and set_text_size is
implementation-dependent.
value text_size : string -> int * int
Return the dimensions of the given text, if it were drawn with the
current font and size.
Filling
value fill_rect : int -> int -> int -> int -> unit
fill_rect x y w h fills the rectangle with lower left corner at x,y,
width w and heigth h, with the current color.
value fill_poly : (int * int) vect -> unit
Fill the given polygon with the current color. The array contains the
coordinates of the vertices of the polygon.
value fill_arc : int -> int -> int -> int -> int -> int -> unit
Fill an elliptical pie slice with the current color. The parameters are
the same as for draw_arc.
value fill_ellipse : int -> int -> int -> int -> unit
Fill an ellipse with the current color. The parameters are the same as
for draw_ellipse.
Chapter 6. The graphics library 81
value fill_circle : int -> int -> int -> unit
Fill a circle with the current color. The parameters are the same as for
draw_circle.
Images
type image
The abstract type for images, in internal representation. Externally,
images are represented as matrices of colors.
value transp : color
In matrices of colors, this color represent a ``transparent'' point:
when drawing the corresponding image, all pixels on the screen
corresponding to a transparent pixel in the image will not be modified,
while other points will be set to the color of the corresponding point in
the image. This allows superimposing an image over an existing
background.
value make_image : color vect vect -> image
Convert the given color matrix to an image. Each sub-array represents
one horizontal line. All sub-arrays must have the same length;
otherwise, exception Graphic_failure is raised.
value dump_image : image -> color vect vect
Convert an image to a color matrix.
value draw_image : image -> int -> int -> unit
Draw the given image with lower left corner at the given point.
value get_image : int -> int -> int -> int -> image
Capture the contents of a rectangle on the screen as an image. The
parameters are the same as for fill_rect.
value create_image : int -> int -> image
create_image w h returns a new image w pixels wide and h pixels tall, to
be used in conjunction with blit_image. The initial image contents are
random.
value blit_image : image -> int -> int -> unit
blit_image img x y copies screen pixels into the image img, modifying img
in-place. The pixels copied are those inside the rectangle with lower
left corner at x,y, and width and height equal to those of the image.
Mouse and keyboard events
type status =
Chapter 6. The graphics library 82
{ mouse_x : int; (* X coordinate of the mouse *)
mouse_y : int; (* Y coordinate of the mouse *)
button : bool; (* true if a mouse button is pressed *)
keypressed : bool; (* true if a key has been pressed *)
key : char } (* the character for the key pressed *)
To report events.
type event =
Button_down (* A mouse button is pressed *)
| Button_up (* A mouse button is released *)
| Key_pressed (* A key is pressed *)
| Mouse_motion (* The mouse is moved *)
| Poll (* Don't wait; return immediately *)
To specify events to wait for.
value wait_next_event : event list -> status
Wait until one of the events specified in the given event list occurs,
and return the status of the mouse and keyboard at that time. If Poll is
given in the event list, return immediately with the current status. If
the mouse cursor is outside of the graphics window, the mouse_x and
mouse_y fields of the event are outside the range
0..size_x()-1, 0..size_y()-1. Keypresses are queued, and dequeued one by
one when the Key_pressed event is specified.
Mouse and keyboard polling
value mouse_pos : unit -> int * int
Return the position of the mouse cursor, relative to the graphics window.
If the mouse cursor is outside of the graphics window, mouse_pos()
returns a point outside of the range 0..size_x()-1, 0..size_y()-1.
value button_down : unit -> bool
Return true if the mouse button is pressed, false otherwise.
value read_key : unit -> char
Wait for a key to be pressed, and return the corresponding character.
Keypresses are queued.
value key_pressed : unit -> bool
Return true if a keypress is available; that is, if read_key would not
block.
Sound
value sound : int -> int -> unit
sound freq dur plays a sound at frequency freq (in hertz) for a duration
dur (in milliseconds). On the Macintosh, for obscure technical reasons,
Chapter 6. The graphics library 83
the frequency is rounded to the nearest note in the equal-tempered scale.
Part IV
The Caml Light commands
84
Chapter 7
Batch compilation (camlc)
This chapter describes how Caml Light programs can be compiled
non-interactively, and turned into standalone executable files. This is
achieved by the command camlc, which compiles and links Caml Light source
files.
Mac: This command is not a standalone Macintosh application. To run camlc,
you need the Macintosh Programmer's Workshop (MPW) programming
environment. The programs generated by camlc are also MPW tools, not
standalone Macintosh applications.
7.1 Overview of the compiler
The camlc command has a command-line interface similar to the one of most C
compilers. It accepts several types of arguments: source files for module
implementations; source files for module interfaces; and compiled module
implementations.
- Arguments ending in .mli are taken to be source files for module
interfaces. Module interfaces declare exported global identifiers,
define public data types, and so on. From the file x.mli, the camlc
compiler produces a compiled interface in the file x.zi.
- Arguments ending in .ml are taken to be source files for module
implementation. Module implementations bind global identifiers to
values, define private data types, and contain expressions to be
evaluated for their side-effects. From the file x.ml, the camlc compiler
produces compiled object code in the file x.zo. If the interface file
x.mli exists, the module implementation x.ml is checked against the
corresponding compiled interface x.zi, which is assumed to exist. If no
interface x.mli is provided, the compilation of x.ml produces a compiled
interface file x.zi in addition to the compiled object code file x.zo.
The produced file x.zi produced corresponds to an interface that exports
everything that is defined in the implementation x.ml.
- Arguments ending in .zo are taken to be compiled object code. These
files are linked together, along with the object code files obtained by
compiling .ml arguments (if any), and the Caml Light standard library, to
produce a standalone executable program. The order in which .zo and .ml
arguments are presented on the command line is relevant: global
identifiers are initialized in that order at run-time, and it is a
link-time error to use a global identifier before having initialized it.
Hence, a given x.zo file must come before all .zo files that refer to
85
Chapter 7. Batch compilation (camlc) 86
identifiers defined in the file x.zo.
The output of the linking phase is a file containing compiled code that can
be executed by the Caml Light runtime system: the command named camlrun. If
caml.out is the name of the file produced by the linking phase, the command
camlrun caml.out arg1 arg2 ... argn
executes the compiled code contained in caml.out, passing it as arguments the
character strings arg1 to argn. (See the chapter on camlrun for more
details.)
Unix: On most Unix systems, the file produced by the linking phase can be run
directly, as in:
./caml.out arg1 arg2 ... argn
The produced file has the executable bit set, and it manages to launch
the bytecode interpreter by itself.
PC: The output file produced by the linking phase is directly executable,
provided it is given extension .EXE. Hence, if the output file is named
caml_out.exe, you can execute it with the command
caml_out arg1 arg2 ... argn
Actually, the produced file caml_out.exe is a tiny executable file
prepended to the bytecode file. The executable simply runs the camlrun
runtime system on the remainder of the file. (As a consequence, this
is not a standalone executable: it still requires camlrun.exe to
reside in one of the directories in the path.)
7.2 Options
The following command-line options are recognized by camlc.
-c Compile only. Suppress the linking phase of the compilation. Source
code files are turned into compiled files, but no executable file is
produced. This option is useful to compile modules separately.
-custom
Link in ``custom runtime'' mode. In the default linking mode, the linker
produces bytecode that is intended to be executed with the shared runtime
system, camlrun. In the custom runtime mode, the linker produces an
output file that contains both the runtime system and the bytecode for
the program. The resulting file is considerably larger, but it can be
executed directly, even if the camlrun command is not installed.
Moreover, the ``custom runtime'' mode enables linking Caml Light code
with user-defined C functions, as described in chapter 12.
Unix: Never strip an executable produced with the -custom option.
PC: This option is not implemented.
Chapter 7. Batch compilation (camlc) 87
Mac: This option is not implemented.
-files response-file
Process the files whose names are listed in file response-file, just as
if these names appeared on the command line. File names in response-file
are separated by blanks (spaces, tabs, newlines). This option allows to
overcome silly limitations on the length of the command line.
-g Cause the compiler to produce additional debugging information. During
the linking phase, this option add information at the end of the
executable bytecode file produced. This information is required in
particular by the catch-all exceptions handlers provided by the module
printexc in the standard library.
During the compilation of an implementation file (.ml file), the compiler
writes a .zix file when the -g option is set. This .zix file describes
the full interface of the .ml file, that is, all types and values defined
in the .ml file, including those that are local to the .ml file (i.e.
not declared in the .mli interface file). Used in conjunction with the
-g option to the toplevel system (chapter ??), the .zix file gives access
to the local values of the module, making it possible to print or
``trace'' them. The .zix file is not produced if the implementation file
has no explicit interface, since, in this case, the module has no local
values.
-i Cause the compiler to print the declared types, exceptions, and global
variables (with their inferred types) when compiling an implementation
(.ml file). This can be useful to check the types inferred by the
compiler. Also, since the output follows the syntax of module
interfaces, it can help in writing an explicit interface (.mli file) for
a file: just redirect the standard output of the compiler to a .mli
file, and edit that file to remove all declarations of unexported
globals.
-I directory
Add the given directory to the list of directories searched for compiled
interface files (.zi) and compiled object code files (.zo). By default,
the current directory is searched first, then the standard library
directory. Directories added with -I are searched after the current
directory, but before the standard library directory. When several
directories are added with several -I options on the command line, these
directories are searched from right to left (the rightmost directory is
searched first, the leftmost is searched last). (Directories can also be
added to the search path from inside the programs with the #directory
directive; see chapter 3.)
-o exec-file
Specify the name of the output file produced by the linker.
Unix: The default output name is a.out, in keeping with the tradition.
PC: The default output name is CAML_OUT.EXE.
Mac: The default output name is Caml.Out.
Chapter 7. Batch compilation (camlc) 88
-O module-set
Specify which set of standard modules is to be implicitly ``opened'' at
the beginning of a compilation. There are three module sets currently
available:
cautious
provides the standard operations on integers, floating-point numbers,
characters, strings, arrays, ..., as well as exception handling,
basic input/output, etc. Operations from the cautious set perform
range and bound checking on string and array operations, as well as
various sanity checks on their arguments.
fast
provides the same operations as the cautious set, but without sanity
checks on their arguments. Programs compiled with -O fast are
therefore slightly faster, but unsafe.
none
suppresses all automatic opening of modules. Compilation starts in
an almost empty environment. This option is not of general use,
except to compile the standard library itself.
The default compilation mode is -O cautious. See chapter 4 for a
complete listing of the modules in the cautious and fast sets.
-v Print the version number the various passes of the compiler.
7.3 Modules and the file system
This short section is intended to clarify the relationship between the names
of the modules and the names of the files that contain their compiled
interface and compiled implementation.
The compiler always derives the name of the compiled module by taking the
base name of the source file (.ml or .mli file). That is, it strips the
leading directory name, if any, as well as the .ml or .mli suffix. The
produced .zi and .zo files have the same base name as the source file; hence,
the compiled files produced by the compiler always have their base name equal
to the name of the module they describe (for .zi files) or implement (for .zo
files).
For compiled interface files (.zi files), this invariant must be preserved
at all times, since the compiler relies on it to load the compiled interface
file for the modules that are used from the module being compiled. Hence, it
is risky and generally incorrect to rename .zi files. It is admissible to
move them to another directory, if their base name is preserved, and the
correct -I options are given to the compiler.
Compiled bytecode files (.zo files), on the other hand, can be freely
renamed once created. That's because 1- .zo files contain the true name of
the module they define, so there is no need to derive that name from the file
name; 2- the linker never attempts to find by itself the .zo file that
implements a module of a given name: it relies on the user providing the list
of .zo files by hand.
Chapter 7. Batch compilation (camlc) 89
7.4 Common errors
This section describes and explains the most frequently encountered error
messages.
Cannot find file filename
The named file could not be found in the current directory, nor in the
directories of the search path. The filename is either a compiled
interface file (.zi file), or a compiled bytecode file (.zo file). If
filename has the format mod.zi, this means you are trying to compile a
file that references identifiers from module mod, but you have not yet
compiled an interface for module mod. Fix: compile mod.mli or mod.ml
first, to create the compiled interface mod.zi.
If filename has the format mod.zo, this means you are trying to link a
bytecode object file that does not exist yet. Fix: compile mod.ml
first.
If your program spans several directories, this error can also appear
because you haven't specified the directories to look into. Fix: add
the correct -I options to the command line.
Corrupted compiled interface file filename
The compiler produces this error when it tries to read a compiled
interface file (.zi file) that has the wrong structure. This means
something went wrong when this .zi file was written: the disk was full,
the compiler was interrupted in the middle of the file creation, and so
on. This error can also appear if a .zi file is modified after its
creation by the compiler. Fix: remove the corrupted .zi file, and
rebuild it.
Expression of type t1 cannot be used with type t2
This is by far the most common type error in programs. Type t1 is the
type inferred for the expression (the part of the program that is
displayed in the error message), by looking at the expression itself.
Type t2 is the type expected by the context of the expression; it is
deduced by looking at how the value of this expression is used in the
rest of the program. If the two types t1 and t2 are not compatible, then
the error above is produced.
In some cases, it is hard to understand why the two types t1 and t2 are
incompatible. For instance, the compiler can report that ``expression of
type foo cannot be used with type foo'', and it really seems that the two
types foo are compatible. This is not always true. Two type
constructors can have the same name, but actually represent different
types. This can happen if a type constructor is redefined. Example:
type foo = A | B;;
let f = function A -> 0 | B -> 1;;
type foo = C | D;;
f C;;
This result in the error message ``expression C of type foo cannot be
used with type foo''.
Chapter 7. Batch compilation (camlc) 90
Incompatible types with the same names can also appear when a module is
changed and recompiled, but some of its clients are not recompiled.
That's because type constructors in .zi files are not represented by
their name (that would not suffice to identify them, because of type
redefinitions), but by unique stamps that are assigned when the type
declaration is compiled. Consider the three modules:
mod1.ml: type t = A | B;;
let f = function A -> 0 | B -> 1;;
mod2.ml: let g x = 1 + mod1__f(x);;
mod3.ml: mod2__g mod1__A;;
Now, assume mod1.ml is changed and recompiled, but mod2.ml is not
recompiled. The recompilation of mod1.ml can change the stamp assigned
to type t. But the interface mod2.zi will still use the old stamp for
mod1__t in the type of mod2__g. Hence, when compiling mod3.ml, the
system complains that the argument type of mod2__g (that is, mod1__t with
the old stamp) is not compatible with the type of mod1__A (that is,
mod1__t with the new stamp). Fix: use make or a similar tool to ensure
that all clients of a module mod are recompiled when the interface mod.zi
changes. To check that the Makefile contains the right dependencies,
remove all .zi files and rebuild the whole program; if no ``Cannot find
file'' error appears, you're all set.
mod__name is referenced before being defined
This error appears when trying to link an incomplete or incorrectly
ordered set of files. Either you have forgotten to provide an
implementation for the module named mod on the command line (typically,
the file named mod.zo, or a library containing that file). Fix: add the
missing .ml or .zo file to the command line. Or, you have provided an
implementation for the module named mod, but it comes too late on the
command line: the implementation of mod must come before all bytecode
object files that reference one of the global variables defined in module
mod. Fix: change the order of .ml and .zo files on the command line.
Of course, you will always encounter this error if you have mutually
recursive functions across modules. That is, function mod1__f calls
function mod2__g, and function mod2__g calls function mod1__f. In this
case, no matter what permutations you perform on the command line, the
program will be rejected at link-time. Fixes:
- Put f and g in the same module.
- Parameterize one function by the other. That is, instead of having
mod1.ml: let f x = ... mod2__g ... ;;
mod2.ml: let g y = ... mod1__f ... ;;
define
Chapter 7. Batch compilation (camlc) 91
mod1.ml: let f g x = ... g ... ;;
mod2.ml: let rec g y = ... mod1__f g ... ;;
and link mod1 before mod2.
- Use a reference to hold one of the two functions, as in :
mod1.ml: let forward_g =
ref((fun x -> failwith "forward_g") : <type>);;
let f x = ... !forward_g ... ;;
mod2.ml: let g y = ... mod1__f ... ;;
mod1__forward_g := g;;
Unavailable C primitive f
This error appears when trying to link code that calls external functions
written in C in ``default runtime'' mode. As explained in chapter 12,
such code must be linked in ``custom runtime'' mode. Fix: add the
-custom option, as well as the (native code) libraries and (native code)
object files that implement the required external functions.
Chapter 8
The toplevel system (camllight)
This chapter describes the toplevel system for Caml Light, that permits
interactive use of the Caml Light system, through a read-eval-print loop. In
this mode, the system repeatedly reads Caml Light phrases from the input, then
typechecks, compile and evaluate them, then prints the inferred type and
result value, if any. The system prints a # (sharp) prompt before reading
each phrase. A phrase can extends several lines; phrases are delimited by ;;
(the final double-semicolon).
From the standpoint of the module system, all phrases entered at toplevel
are treated as the implementation of a module named top. Hence, all toplevel
definitions are entered in the module top.
Unix: The toplevel system is started by the command camllight. Phrases are
read on standard input, results are printed on standard output, errors
on standard error. End-of-file on standard input terminates camllight
(see also the quit system function below).
The toplevel system does not perform line editing, but it can easily be
used in conjunction with an external line editor such as fep; just run
fep -emacs camllight or fep -vi camllight.
At any point, the parsing, compilation or evaluation of the current
phrase can be interrupted by pressing ctrl-C (or, more precisely, by
sending the intr signal to the camllight process). This goes back to
the # prompt.
Mac: The toplevel system is presented as the standalone Macintosh
application Caml Light. This application does not require the
Macintosh Programmer's Workshop to run.
Once launched from the Finder, the application opens two windows,
``Caml Light Input'' and ``Caml Light Output''. Phrases are entered in
the ``Caml Light Input'' window. The ``Caml Light Output'' window
displays a copy of the input phrases as they are processed by the Caml
Light toplevel, interspersed with the toplevel responses. The
``Return'' key sends the contents of the Input window to the Caml Light
toplevel. The ``Enter'' key inserts a newline without sending the
contents of the Input window. (This can be configured with the
``Preferences'' menu item.)
The contents of the input window can be edited at all times, with the
standard Macintosh interface. An history of previously entered phrases
is maintained, and can be accessed with the ``Previous entry''
(command-P) and ``Next entry'' (command-N) menu items.
92
Chapter 8. The toplevel system (camllight) 93
To quit the Caml Light application, either select ``Quit'' from the
``Files'' menu, or use the quit function described below.
At any point, the parsing, compilation or evaluation of the current
phrase can be interrupted by pressing ``command-dot'', or by selecting
the item ``Interrupt Caml Light'' in the ``Caml Light'' menu. This
goes back to the # prompt.
PC: The toplevel system is started by the command caml. (The full name
camllight had to be truncated because of the well-known limitations of
MS-DOS.) Phrases are read on standard input, results are printed on
standard output, errors on standard error. The quit system function
terminates caml.
A number of TSR line editors that provide line editing and history
facilities for the command.com command-line interpreter also work in
conjunction with caml. Some TSR's that work: dosedit, ced, toddy.
Some TSR's that don't work: doskey from the MS-DOS 5.0 distribution.
With the 8086 version, the parsing, compilation or evaluation of the
current phrase can be interrupted by pressing ctrl-break. This goes
back to the # prompt. Pressing ctrl-C interrupts input, but does not
stop a phrase that performs no input-output.
With the 80386 version, pressing ctrl-C or ctrl-break interrupts the
system at any point: during parsing as well as during compilation or
evaluation.
8.1 Options
The following command-line options are recognized by the caml or camllight
commands.
-g Start the toplevel system in debugging mode. This mode gives access to
values and types that are local to a module, that is, not exported by the
interface of the module. When debugging mode is off, these local objects
are not accessible (attempts to access them produce an ``Unbound
identifier'' error). When debugging mode is on, these objects become
visible, just like the objects that are exported in the module interface.
In particular, values of abstract types are printed using their concrete
representations, and the functions local to a module can be ``traced''
(see the trace function in section ??). This applies only to the modules
that have been compiled in debugging mode (either by the batch compiler
with the -g option, or by the toplevel system in debugging mode), that
is, those modules that have an associated .zix file.
-I directory
Add the given directory to the list of directories searched for compiled
interface files (.zi) and compiled object code files (.zo). By default,
the current directory is searched first, then the standard library
directory. Directories added with -I are searched after the current
directory, but before the standard library directory. When several
directories are added with several -I options on the command line, these
directories are searched from right to left (the rightmost directory is
searched first, the leftmost is searched last). Directories can also be
added to the search path once the toplevel is running with the #directory
directive; see chapter 3.
Chapter 8. The toplevel system (camllight) 94
-O module-set
Specify which set of standard modules is to be implicitly ``opened'' when
the toplevel starts. There are three module sets currently available:
cautious
provides the standard operations on integers, floating-point numbers,
characters, strings, arrays, ..., as well as exception handling,
basic input/output, ...Operations from the cautious set perform range
and bound checking on string and vector operations, as well as
various sanity checks on their arguments.
fast
provides the same operations as the cautious set, but without sanity
checks on their arguments. Programs compiled with -O fast are
therefore slightly faster, but unsafe.
none
suppresses all automatic opening of modules. Compilation starts in
an almost empty environment. This option is not of general use.
The default compilation mode is -O cautious. See chapter 4 for a
complete listing of the modules in the cautious and fast sets.
8.2 Toplevel control functions
The standard library module toplevel, opened by default when the toplevel
system is launched, provides a number of functions that control the toplevel
behavior, load files in memory, and trace program execution.
quit ()
Exit the toplevel loop and terminate the Caml Light command.
include "filename"
Read, compile and execute source phrases from the file filename. The .ml
extension is automatically added to filename, if not present. This is
textual inclusion: phrases are processed just as if they were typed on
standard input. In particular, global identifiers defined by these
phrases are entered in the module named top, not in a new module.
load "filename"
Load in memory the source code for a module implementation. Read,
compile and execute source phrases from file filename. The .ml extension
is automatically added to filename, if not present. The load function
behaves much like include, except that a new module is created, with name
the base name of filename. Global identifiers defined in file filename
are entered in this module, instead of the top module as in the case of
include. For instance, assuming file foo.ml contains the single phrase
let bar = 1;;
executing load "foo" defines the identifier foo__bar with value 1.
Chapter 8. The toplevel system (camllight) 95
Caveat: the loaded module is not automatically opened: the identifier
bar does not automatically complete to foo__bar. To achieve this, you
must execute the directive #open "foo" afterwards.
compile "filename"
Compile the source code for a module implementation or interface (.ml or
.mli file). Compilation proceeds as with the batch compiler, and
produces the same results as camlc -c filename. If the toplevel system
is in debugging mode (option -g or function debug_mode below), the
compilation is also performed in debugging mode, as when giving the -g
option to the batch compiler. The result of the compilation is left in
files (.zo, .zi, .zix). The compiled code is not loaded in memory.
load_object "filename"
Load in memory the compiled bytecode contained in file filename. The .zo
extension is automatically added to filename, if not present. The
bytecode file has been produced by the standalone compiler camlc. Global
identifiers defined in file filename are entered in their own module, not
in the top module, just as with the load function.
trace "function-name"
After the execution of trace "foo", all calls to the global function
named foo will be ``traced''. That is, the argument and the result are
displayed for each call, as well as the exceptions escaping out of foo,
either raised by foo itself, or raised by one of the functions called
from foo. If foo is a curried function, each argument is printed as it
is passed to the function.
untrace "function-name"
Executing untrace "foo" stops all tracing over the global function named
foo.
debug_mode boolean-flag
Set the debugging mode on (debug_mode true) or off (debug_mode false).
Executing debug_mode true is equivalent to starting the toplevel system
with the -g option. In debugging mode, values and types local to a
module (not exported by its interface) are visible, just like the
exported values and types. See the description of the -g option in
section ??.
verbose_mode boolean-flag
After executing verbose_mode true, the compilations performed by compile
print the objects defined by the module, along with their types, just as
with the -i option to the batch compiler. To revert to silent
compilations, execute verbose_mode false.
cd "directory-name"
Set the current working directory.
gc ()
Finish the current garbage collection cycle, and return the amount of
free space in the heap, in bytes. If you want to perform a complete GC
cycle, call this function twice.
Chapter 8. The toplevel system (camllight) 96
8.3 The toplevel and the module system
Toplevel phrases can refer to identifiers defined in modules other than the
top module with the same mechanisms as for separately compiled modules:
either by using qualified identifiers (modulename__localname), or by using
unqualified identifiers that are automatically completed by searching the list
of opened modules. (See section 2 of the reference manual.) The modules
opened at startup are given in the documentation for the standard library.
Other modules can be opened with the #open directive.
However, before referencing a global variable from a module other than the
top module, a definition of that global variable must have been entered in
memory. At start-up, the toplevel system contains the definitions for all the
identifiers in the standard library. The definitions for user modules can be
entered with the load or load_object functions described above. Referencing a
global variable for which no definition has been provided by load or
load_object results in the error ``Identifier foo__bar is referenced before
being defined''. Since this is a tricky point, let us consider some examples.
1. The library function sub_string is defined in module string. This module
is part of the standard library, and is one of the modules automatically
opened at start-up. Hence, both phrases
sub_string "qwerty" 1 3;;
string__sub_string "qwerty" 1 3;;
are correct, without having to use #open, load, or load_object.
2. The library function printf is defined in module printf. This module is
part of the standard library, but it is not automatically opened at
start-up. Hence, the phrase
printf__printf "%s %s" "hello" "world";;
is correctly executed, while
printf "%s %s" "hello" "world";;
causes the error ``Variable printf is unbound'', since none of the
currently opened modules define a global with local name printf.
However,
#open "printf";;
printf "%s %s" "hello" "world";;
executes correctly.
3. Assume the file foo.ml resides in the current directory, and contains the
single phrase
Chapter 8. The toplevel system (camllight) 97
let x = 1;;
When the toplevel starts, references to x will cause the error ``Variable
x is unbound''. References to foo__x will cause the error ``Cannot find
file foo.zi'', since the typechecker is attempting to load the compiled
interface for module foo in order to find the type of x. To load in
memory the module foo, just do:
load "foo";;
Then, references to foo__x typecheck and evaluate correctly. Since load
does not open the module it loads, references to x will still fail with
the error ``Variable x is unbound''. You will have to do
#open "foo";;
explicitly, for x to complete automatically into foo__x.
4. Finally, assume the file foo.ml above has been previously compiled with
the camlc -c command. The current directory therefore contains a
compiled interface foo.zi, claiming that foo__x is a global variable with
type int, and a compiled bytecode file foo.zo, defining foo__x to have
the value 1. When the toplevel starts, references to foo__x will cause
the error ``foo__x is referenced before being defined''. In contrast
with case 3 above, the typechecker has succeeded in finding the compiled
interface for module foo. But execution cannot proceed, because no
definition for foo__x has been entered in memory. To do so, execute:
load_object "foo";;
This loads the file foo.zo in memory, therefore defining foo__x. Then,
references to foo__x evaluate correctly. As in case 3 above, references
to x still fail, because load_object does not open the module it loads.
Again, you will have to do
#open "foo";;
explicitly, for x to complete automatically into foo__x.
8.4 Common errors
This section describes and explains the most frequently encountered error
messages.
Cannot find file filename
The named file could not be found in the current directory, nor in the
directories of the search path.
Chapter 8. The toplevel system (camllight) 98
If filename has the format mod.zi, this means the current phrase
references identifiers from module mod, but you have not yet compiled an
interface for module mod. Fix: either load the file mod.ml, which will
also create in memory the compiled interface for module mod; or use camlc
to compile mod.mli or mod.ml, creating the compiled interface mod.zi,
before you start the toplevel.
If filename has the format mod.zo, this means you are trying to load with
load_object a bytecode object file that does not exist yet. Fix:
compile mod.ml with camlc before you start the toplevel. Or, use load
instead of load_object to load the source code instead of a compiled
object file.
If filename has the format mod.ml, this means load or include could not
find the specified source file. Fix: check the spelling of the file
name, or write it if it does not exist.
mod__name is referenced before being defined
You have neglected to load in memory an implementation for a module, with
load or load_object. This is explained in full detail in section 8.3
above.
Corrupted compiled interface file filename
See section 7.4.
Expression of type t1 cannot be used with type t2
See section 7.4.
8.5 Building custom toplevel systems: camlmktop
The camlmktop command builds Caml Light toplevels that contain user code
preloaded at start-up.
Mac: This command is not available in the Macintosh version.
PC: This command is not available in the PC versions.
The camlmktop command takes as argument a set of .zo files, and links them
with the object files that implement the Caml Light toplevel. The typical use
is:
camlmktop -o mytoplevel foo.zo bar.zo gee.zo
This creates the bytecode file mytoplevel, containing the Caml Light toplevel
system, plus the code from the three .zo files. To run this toplevel, give it
as argument to the camllight command:
camllight mytoplevel
This starts a regular toplevel loop, except that the code from foo.zo, bar.zo
and gee.zo is already loaded in memory, just as if you had typed:
load_object "foo";;
load_object "bar";;
load_object "gee";;
Chapter 8. The toplevel system (camllight) 99
on entrance to the toplevel. The modules foo, bar and gee are not opened,
though; you still have to do
#open "foo";;
yourself, if this is what you wish.
8.6 Options
The following command-line options are recognized by camlmktop.
-custom
Link in ``custom runtime'' mode. See the corresponding option for camlc,
in chapter 7.
-I directory
Add the given directory to the list of directories searched for compiled
object code files (.zo).
-o exec-file
Specify the name of the toplevel file produced by the linker. The
default is camltop.out.
Chapter 9
The runtime system (camlrun)
The camlrun command executes bytecode files produced by the linking phase of
the camlc command.
Mac: This command is a MPW tool, not a standalone Macintosh application.
9.1 Overview
The camlrun command comprises three main parts: the bytecode interpreter,
that actually executes bytecode files; the memory allocator and garbage
collector; and a set of C functions that implement primitive operations such
as input/output.
The usage for camlrun is:
camlrun options bytecode-executable arg1 arg2 ... argn
The first non-option argument is taken to be the name of the file containing
the executable bytecode. (That file is searched in the executable path as
well as in the current directory.) The remaining arguments are passed to the
Caml Light program, in the string array sys__command_line. Element 0 of this
array is the name of the bytecode executable file; elements 1 to n are the
remaining arguments arg1 to argn.
As mentioned in chapter 7, in most cases, the bytecode executable files
produced by the camlc command are self-executable, and manage to launch the
camlrun command on themselves automatically. That is, assuming caml.out is a
bytecode executable file,
caml.out arg1 arg2 ... argn
works exactly as
camlrun caml.out arg1 arg2 ... argn
Notice that it is not possible to pass options to camlrun when invoking
directly caml.out.
9.2 Options
The following command-line option is recognized by camlrun. (There are
additional options to control the behavior of the garbage collector, but they
are not for the casual user.)
100
Chapter 9. The runtime system (camlrun) 101
-v Cause camlrun to print various diagnostic messages relative to memory
allocation and garbage collection. Useful to debug memory-related
problems.
9.3 Common errors
This section describes and explains the most frequently encountered error
messages.
filename: no such file or directory
If filename is the name of a self-executable bytecode file, this means
that either that file does not exist, or that it failed to run the
camlrun bytecode interpreter on itself. The second possibility indicates
that Caml Light has not been properly installed on your system.
Cannot exec camlrun
(When launching a self-executable bytecode file.) The camlrun command
could not be found in the executable path. Check that Caml Light has
been properly installed on your system.
Cannot find the bytecode file
The file that camlrun is trying to execute (e.g. the file given as first
non-option argument to camlrun) either does not exist, or is not a valid
executable bytecode file.
Truncated bytecode file
The file that camlrun is trying to execute is not a valid executable
bytecode file. Probably it has been truncated or mangled since created.
Erase and rebuild it.
Uncaught exception
The program being executed contains a ``stray'' exception. That is, it
raises an exception at some point, and this exception is never caught.
This causes immediate termination of the program. If you wish to know
which exception thus escapes, use the printexc__f function from the
standard library (and don't forget to link your program with the -g
option).
Out of memory
The program being executed requires more memory than available. Either
the program builds too large data structures; or the program contains too
many nested function calls, and the stack overflows. In some cases, your
program is perfectly correct, it just requires more memory than your
machine provides. (This happens quite frequently on small
microcomputers, but is unlikely on Unix machines.) In other cases, the
``out of memory'' message reveals an error in your program:
non-terminating recursive function, allocation of an excessively large
array or string, attempts to build an infinite list or other data
structure, ...
To help you diagnose this error, run your program with the -v option to
camlrun. If it displays lots of ``Growing stack...'' messages, this is
probably a looping recursive function. If it displays lots of ``Growing
heap...'' messages, with the heap size growing slowly, this is probably
an attempt to construct a data structure with too many (infinitely many?)
cells. If it displays few ``Growing heap...'' messages, but with a huge
increment in the heap size, this is probably an attempt to build an
Chapter 9. The runtime system (camlrun) 102
excessively large array or string.
Chapter 10
The librarian (camllibr)
Mac: This command is a MPW tool, not a standalone Macintosh application.
10.1 Overview
The camllibr program packs in one single file a set of bytecode object files
(.zo files). The resulting file is also a bytecode object file and also has
the .zo extension. It can be passed to the link phase of the camlc compiler
in replacement of the original set of bytecode object files. That is, after
running
camllibr -o library.zo mod1.zo mod2.zo mod3.zi mod4.zo
all calls to the linker with the form
camlc ... library.zo ...
are exactly equivalent to
camlc ... mod1.zo mod2.zo mod3.zi mod4.zo ...
The typical use of camllibr is to build a library composed of several
modules: this way, users of the library have only one .zo file to specify on
the command line to camlc, instead of a bunch of .zo files, one per module
contained in the library.
The linking phase of camlc is clever enough to discard the code
corresponding to useless phrases: in particular, definitions for global
variables that are never used after their definitions. Hence, there is no
problem with putting many modules, even rarely used ones, into one single
library: this will not result in bigger executables.
The usage for camllibr is:
camllibr options file1 .zo...filen.zo
where file1.zo through filen.zo are the object files to pack together. The
order in which these file names are presented on the command line is relevant:
the compiled phrases contained in the library will be executed in that order.
(Remember that it is a link-time error to refer to a global variable that has
not yet been defined.)
10.2 Options
The following command-line options are recognized by camllibr.
103
Chapter 10. The librarian (camllibr) 104
-files response-file
Process the files whose names are listed in file response-file, just as
if these names appeared on the command line. File names in response-file
are separated by blanks (spaces, tabs, newlines). This option allows to
overcome silly limitations on the length of the command line.
-I directory
Add the given directory to the list of directories searched for the input
.zo files. By default, the current directory is searched first, then the
standard library directory. Directories added with -I are searched after
the current directory, but before the standard library directory. When
several directories are added with several -I options on the command
line, these directories are searched from right to left (the rightmost
directory is searched first, the leftmost is searched last).
-o library-name
Specify the name of the output file. The default is library.zo.
10.3 Turning code into a library
To develop a library, it is usually more convenient to split it into several
modules, that reflect the internal structure of the library. From the
standpoint of the library users, however, it is preferable to view the library
as a single module, with only one interface file (.zi file) and one
implementation file (.zo file): linking is easier, and there is no need to
put a bunch of #open directives, nor to have to remember the internal
structure of the library.
The camllibr command allows having a single .zo file for the whole library.
Here is how the Caml Light module system can be used (some say ``abused'') to
have a single .zi file for the whole library. To be more concrete, assume
that the library comprises three modules, windows, images and buttons. The
idea is to add a fourth module, mylib, that re-exports the public parts of
windows, images and buttons. The interface mylib.mli contains definitions for
those types that are public (exported with their definitions), declarations
for those types that are abstract (exported without their definitions), and
declarations for the functions that can be called from the user's code:
(* File mylib.mli *)
type 'a option = None | Some of 'a;; (* a public type *)
type window and image and button;; (* three abstract types *)
value new_window : int -> int -> window (* the public functions *)
and draw_image : image -> window -> int -> int -> unit
and ...
The implementation of the mylib module simply equates the abstract types and
the public functions to the corresponding types and functions in the modules
windows, images and buttons:
(* File mylib.ml *)
type window == windows__win
and image == images__pixmap
and button == buttons__t;;
let new_window = windows__open_window
and draw_image = images__draw
and ...
The files windows.ml, images.ml and buttons.ml can open the mylib module, to
Chapter 10. The librarian (camllibr) 105
access the public types defined in the interface mylib.mli, such as the option
type. Of course, these modules must not reference the abstract types nor the
public functions, to avoid circularities.
Types such as windows__win in the example above can be exported by the
windows module either abstractly or concretely (with their definition).
Often, it is necessary to export them concretely, because the other modules in
the library (images, buttons) need to build or destructure directly values of
that type. Even if windows__win is exported concretely by the windows module,
that type will remain abstract to the library user, since it is abstracted by
the public interface mylib.
The actual building of the library mylib proceeds as follows:
camlc -c mylib.mli # create mylib.zi
camlc -c windows.mli windows.ml images.mli images.ml
camlc -c buttons.mli buttons.ml
camlc -c mylib.ml # create mylib.zo
mv mylib.zo tmplib.zo # renaming to avoid overwriting mylib.zo
camllibr -o mylib.zo windows.zo images.zo buttons.zo tmplib.zo
Then, copy mylib.zi and mylib.zo to a place accessible to the library users.
The other .zi and .zo files need not be copied.
Chapter 11
Lexer and parser generators (camllex, camlyacc)
This chapter describes two program generators: camllex, that produces a
lexical analyzer from a set of regular expressions with associated semantic
actions, and camlyacc, that produces a parser from a grammar with associated
semantic actions.
These program generators are very close to the well-known lex and yacc
commands that can be found in most C programming environments. This chapter
assumes a working knowledge of lex and yacc: while it describes the input
syntax for camllex and camlyacc and the main differences with lex and yacc, it
does not explain the basics of writing a lexer or parser description in lex
and yacc. Readers unfamiliar with lex and yacc are referred to ``Compilers:
principles, techniques, and tools'' by Aho, Sethi and Ullman (Addison-Wesley,
1986), ``Compiler design in C'' by Holub (Prentice-Hall, 1990), or ``Lex &
Yacc'', by Mason and Brown (O'Reilly, 1990).
Streams and stream matching, as described in chapter ??, provide an
alternative way to write lexers and parsers. The stream matching technique is
more powerful than the combination of camllex and camlyacc in some cases
(higher-order parsers), but less powerful in other cases (precedences).
Choose whichever approach is more adapted to your parsing problem.
Mac: These commands are MPW tool, not standalone Macintosh applications.
86: These commands are not available in the 8086 PC version.
11.1 Overview of camllex
The camllex command produces a lexical analyzer from a set of regular
expressions with attached semantic actions, in the style of lex. Assuming the
input file is lexer.mll, executing
camllex lexer.mll
produces Caml Light code for a lexical analyzer in file lexer.ml. This file
defines one lexing function per entry point in the lexer definition. These
functions have the same names as the entry points. Lexing functions take as
argument a lexer buffer, and return the semantic attribute of the
corresponding entry point.
Lexer buffers are an abstract data type implemented in the standard library
module lexing. The functions create_lexer_channel, create_lexer_string and
create_lexer from module lexing create lexer buffers that read from an input
channel, a character string, or any reading function, respectively. (See the
description of module lexing in chapter 4.)
When used in conjunction with a parser generated by camlyacc, the semantic
106
Chapter 11. Lexer and parser generators (camllex, camlyacc) 107
actions compute a value belonging to the type token defined by the generated
parsing module. (See the description of camlyacc below.)
11.2 Syntax of lexer definitions
The format of lexer definitions is as follows:
{ header }
rule entrypoint =
parse regexp { action }
| ...
| regexp { action }
and entrypoint =
parse ...
and ...
;;
Comments are delimited by (* and *), as in Caml Light.
11.2.1 Header
The header section is arbitrary Caml Light text enclosed in curly braces. It
can be omitted. If it is present, the enclosed text is copied as is at the
beginning of the output file. Typically, the header section contains the
#open directives required by the actions, and possibly some auxiliary
functions used in the actions.
11.2.2 Entry points
The names of the entry points must be valid Caml Light identifiers.
11.2.3 Regular expressions
The regular expressions are in the style of lex, with a more Caml-like syntax.
` char `
A character constant, with the same syntax as Caml Light character
constants. Match the denoted character.
_ Match any character.
eof Match the end of the lexer input.
" string "
A string constant, with the same syntax as Caml Light string constants.
Match the corresponding sequence of characters.
[ character-set ]
Match any single character belonging to the given character set. Valid
character sets are: single character constants ` c `; ranges of
characters ` c_1 ` - ` c_2 ` (all characters between c1 and c2,
inclusive); and the union of two or more character sets, denoted by
concatenation.
[ ^ character-set ]
Match any single character not belonging to the given character set.
Chapter 11. Lexer and parser generators (camllex, camlyacc) 108
regexp *
(Repetition.) Match the concatenation of zero or more strings that match
regexp.
regexp +
(Strict repetition.) Match the concatenation of one or more strings that
match regexp.
regexp ?
(Option.) Match either the empty string, or a string matching regexp.
regexp_1 | regexp_2
(Alternative.) Match any string that matches either regexp_1 or regexp_2
regexp_1 regexp_2
(Concatenation.) Match the concatenation of two strings, the first
matching regexp_1, the second matching regexp_2.
( regexp )
Match the same strings as regexp.
Concerning the precedences of operators, * and + have highest precedence,
followed by ?, then concatenation, then | (alternation).
11.2.4 Actions
The actions are arbitrary Caml Light expressions. They are evaluated in a
context where the identifier lexbuf is bound to the current lexer buffer.
Some typical uses for lexbuf, in conjunction with the operations on lexer
buffers provided by the lexing standard library module, are listed below.
lexing__get_lexeme lexbuf
Return the matched string.
lexing__get_lexeme_char lexbuf n
th
Return the n character in the matched string. The first character
corresponds to n=0.
lexing__get_lexeme_start lexbuf
Return the absolute position in the input text of the beginning of the
matched string. The first character read from the input text has
position 0.
lexing__get_lexeme_end lexbuf
Return the absolute position in the input text of the end of the matched
string. The first character read from the input text has position 0.
entrypoint lexbuf
(Where entrypoint is the name of another entry point in the same lexer
definition.) Recursively call the lexer on the given entry point.
Useful for lexing nested comments, for example.
11.3 Overview of camlyacc
The camlyacc command produces a parser from a context-free grammar
specification with attached semantic actions, in the style of yacc. Assuming
Chapter 11. Lexer and parser generators (camllex, camlyacc) 109
the input file is grammar.mly, executing
camlyacc options grammar.mly
produces Caml Light code for a parser in the file grammar.ml, and its
interface in file grammar.mli.
The generated module defines one parsing function per entry point in the
grammar. These functions have the same names as the entry points. Parsing
functions take as arguments a lexical analyzer (a function from lexer buffers
to tokens) and a lexer buffer, and return the semantic attribute of the
corresponding entry point. Lexical analyzer functions are usually generated
from a lexer specification by the camllex program. Lexer buffers are an
abstract data type implemented in the standard library module lexing. Tokens
are values from the concrete type token, defined in the interface file
grammar.mli produced by camlyacc.
11.4 Syntax of grammar definitions
Grammar definitions have the following format:
%{
header
%}
declarations
%%
rules
%%
trailer
Comments are enclosed between /* and */ pairs, as in C, except in the header
and trailer sections.
11.4.1 Header and trailer
The header and the trailer sections are Caml Light code that is copied as is
into file grammar.ml. Both sections are optional. The header goes at the
beginning of the output file; it usually contains #open directives required by
the semantic actions of the rules. The trailer goes at the end of the output
file.
11.4.2 Declarations
Declarations are given one per line. They all start with a % sign.
%token symbol...symbol
Declare the given symbols as tokens (terminal symbols). These symbols
are added as constant constructors for the token concrete type.
%token < type > symbol...symbol
Declare the given symbols as tokens with an attached attribute of the
given type. These symbols are added as constructors with arguments of
the given type for the token concrete type. The type part is an
arbitrary Caml Light type expression, except that all type constructor
names must be fully qualified (e.g. modname__typename) for all types
except standard built-in types, even if the proper #open directives (e.g.
#open "modname") were given in the header section. That's because the
header is copied only to the .ml output file, but not to the .mli output
Chapter 11. Lexer and parser generators (camllex, camlyacc) 110
file, while the type part of a %token declaration is copied to both.
%start symbol...symbol
Declare the given symbols as entry points for the grammar. For each
entry point, a parsing function with the same name is defined in the
output module. Non-terminals that are not declared as entry points have
no such parsing function. Start symbols must be given a type with the
%type directive below.
%type < type > symbol...symbol
Specify the type of the semantic attributes for the given symbols. This
is mandatory for start symbols only. Other nonterminal symbols need not
be given types by hand: these types will be inferred when running the
output files through the Caml Light compiler (unless the -s option is in
effect). The type part is an arbitrary Caml Light type expression,
except that all type constructor names must be fully qualified (e.g.
modname__typename) for all types except standard built-in types, even if
the proper #open directives (e.g. #open "modname") were given in the
header section. That's because the header is copied only to the .ml
output file, but not to the .mli output file, while the type part of a
%token declaration is copied to both.
%left symbol...symbol
%right symbol...symbol
%nonassoc symbol...symbol
Associate precedences and associativities to the given symbols. All
symbols on the same line are given the same precedence. They have higher
precedence than symbols declared before in a %left, %right or %nonassoc
line. They have lower precedence than symbols declared after in a %left,
%right or %nonassoc line. The symbols are declared to associate to the
left (%left), to the right (%right), or to be non-associative
(%nonassoc). The symbols are usually tokens. They can also be dummy
nonterminals, for use with the %prec directive inside the rules.
11.4.3 Rules
The syntax for rules is as usual:
nonterminal :
symbol ...symbol { semantic-action }
| ...
| symbol ...symbol { semantic-action }
;
Rules can also contain the %prec symbol directive in the right-hand side part,
to override the default precedence and associativity of the rule with the
precedence and associativity of the given symbol.
Semantic actions are arbitrary Caml Light expressions, that are evaluated to
produce the semantic attribute attached to the defined nonterminal. The
semantic actions can access the semantic attributes of the symbols in the
right-hand side of the rule with the $ notation: $1 is the attribute for the
first (leftmost) symbol, $2 is the attribute for the second symbol, etc.
Chapter 11. Lexer and parser generators (camllex, camlyacc) 111
Actions occurring in the middle of rules are not supported. Error recovery
is not implemented.
11.5 Options
The camlyacc command recognizes the following options:
-v Generate a description of the parsing tables and a report on conflicts
resulting from ambiguities in the grammar. The description is put in
file grammar.output.
-s Generate a grammar.ml file with smaller phrases. Semantic actions are
presented in the grammar.ml output file as one large vector of functions.
By default, this vector is built by a single phrase. When the grammar is
large, or contains complicated semantic actions, the resulting phrase may
require large amounts of memory to be compiled by Caml Light. With the
-s option, the vector of actions is constructed incrementally, one phrase
per action. This lowers the memory requirements for the compiler, but it
is no longer possible to infer the types of nonterminal symbols:
typechecking is turned off on symbols that do not have a type specified
by a %type directive.
-bprefix
Name the output files prefix.ml, prefix.mli, prefix.output, instead of
the default naming convention.
11.6 A complete example
The all-time favorite: a desk calculator. This program reads arithmetic
expressions on standard input, one per line, and prints their values. Here is
the grammar definition:
/* File parser.mly */
%token <int> INT
%token PLUS MINUS TIMES DIV
%token LPAREN RPAREN
%token EOL
%left PLUS MINUS /* lowest precedence */
%left TIMES DIV /* medium precedence */
%nonassoc UMINUS /* highest precedence */
%start Main /* the entry point */
%type <int> Main
%%
Main:
Expr EOL { $1 }
;
Expr:
INT { $1 }
| LPAREN Expr RPAREN { $2 }
| Expr PLUS Expr { $1 + $3 }
| Expr MINUS Expr { $1 - $3 }
| Expr TIMES Expr { $1 * $3 }
| Expr DIV Expr { $1 / $3 }
| MINUS Expr %prec UMINUS { - $2 }
;
Here is the definition for the corresponding lexer:
Chapter 11. Lexer and parser generators (camllex, camlyacc) 112
(* File lexer.mll *)
{
#open "parser";; (* The type token is defined in parser.mli *)
exception Eof;;
}
rule Token = parse
[` ` `\t`] { Token lexbuf } (* skip blanks *)
| [`\n` ] { EOL }
| [`0`-`9`]+ { INT(int_of_string (get_lexeme lexbuf)) }
| `+` { PLUS }
| `-` { MINUS }
| `*` { TIMES }
| `/` { DIV }
| `(` { LPAREN }
| `)` { RPAREN }
| eof { raise Eof }
;;
Here is the main program, that combines the parser with the lexer:
(* File calc.ml *)
try
let lexbuf = lexing__create_lexer_channel std_in in
while true do
let result = parser__Main lexer__Token lexbuf in
print_int result; print_newline(); flush std_out
done
with Eof ->
()
;;
To compile everything, execute:
camllex lexer.mll # generates lexer.ml
camlyacc parser.mly # generates parser.ml and parser.mli
camlc -c parser.mli
camlc -c lexer.ml
camlc -c parser.ml
camlc -c calc.ml
camlc -o calc lexer.zo parser.zo calc.zo
Chapter 12
Interfacing C with Caml Light
This chapter describes how user-defined primitives, written in C, can be added
to the Caml Light runtime system and called from Caml Light code.
Mac: This facility is not implemented in the Macintosh version.
PC: This facility is not implemented in the PC versions.
12.1 Overview and compilation information
12.1.1 Declaring primitives
User primitives are declared in a module interface (a .mli file), in the same
way as a regular ML value, except that the declaration is followed by the =
sign, the function arity (number of arguments), and the name of the
corresponding C function. For instance, here is how the input primitive is
declared in the interface for the standard library module io:
value input : in_channel -> string -> int -> int -> int
= 4 "input"
Primitives with several arguments are always curried. The C function does not
necessarily have the same name as the ML function.
Values thus declared primitive in a module interface must not be implemented
in the module implementation (the .ml file). They can be used inside the
module implementation.
12.1.2 Implementing primitives
User primitives with arity n<5 are implemented by C functions that take n
arguments of type value, and return a result of type value. The type value is
the type of the representations for Caml Light values. It encodes objects of
several base types (integers, floating-point numbers, strings, ...), as well
as Caml Light data structures. The type value and the associated conversion
functions and macros are described in details below. For instance, here is
the declaration for the C function implementing the input primitive:
value input(channel, buffer, offset, length)
value channel, buffer, offset, length;
{
...
}
113
Chapter 12. Interfacing C with Caml Light 114
When the primitive function is applied in a Caml Light program, the C
function is called with the values of the expressions to which the primitive
is applied as arguments. The value returned by the function is passed back to
the Caml Light program as the result of the function application.
User primitives with arity greater than 5 are implemented by C functions
that receive two arguments: a pointer to an array of Caml Light values (the
values for the arguments), and an integer which is the number of arguments
provided:
value prim_with_lots_of_args(argv, argn)
value * argv;
int argn;
{
... argv[0] ...; /* The first argument */
... argv[6] ...; /* The seventh argument */
}
Implementing a user primitive is actually two separate tasks: on the one
hand, decoding the arguments to extract C values from the given Caml Light
values, and encoding the return value as a Caml Light value; on the other
hand, actually computing the result from the arguments. Except for very
simple primitives, it is often preferable to have two distinct C functions to
implement these two tasks. The first function actually implements the
primitive, taking native C values as arguments and returning a native C value.
The second function, often called the ``stub code'', is a simple wrapper
around the first function that converts its arguments from Caml Light values
to C values, call the first function, and convert the returned C value to Caml
Light value. For instance, here is the stub code for the input primitive:
value input(channel, buffer, offset, length)
value channel, buffer, offset, length;
{
return Val_long(getblock((struct channel *) channel,
&Byte(buffer, Long_val(offset)),
Long_val(length)));
}
(Here, Val_long, Long_val and so on are conversion macros for the type value,
that will be described later.) The hard work is performed by the function
getblock, which is declared as:
long getblock(channel, p, n)
struct channel * channel;
char * p;
long n;
{
...
}
To write C code that operates on Caml Light values, the following include
files are provided:
mlvalues.h definition of the value type, and conversion macros
alloc.h allocation functions (to create structured Caml Light
objects)
memory.h miscellaneous memory-related functions (for in-place
modification of structures, etc).
Chapter 12. Interfacing C with Caml Light 115
These files reside in the Caml Light standard library directory (usually
/usr/local/lib/caml-light).
12.1.3 Linking C code with Caml Light code
The Caml Light runtime system comprises three main parts: the bytecode
interpreter, the memory manager, and a set of C functions that implement the
primitive operations. Some bytecode instructions are provided to call these C
functions, designated by their offset in a table of functions (the table of
primitives).
In the default mode, the Caml Light linker produces bytecode for the
standard runtime system, with a standard set of primitives. References to
primitives that are not in this standard set result in the ``unavailable C
primitive'' error.
In the ``custom runtime'' mode, the Caml Light linker scans the bytecode
object files (.zo files) and determines the set of required primitives. Then,
it builds a suitable runtime system, by calling the native code linker with:
- the table of the required primitives
- a library that provides the bytecode interpreter, the memory manager, and
the standard primitives
- libraries and object code files (.o files) mentioned on the command line
for the Caml Light linker, that provide implementations for the user's
primitives.
This builds a runtime system with the required primitives. The Caml Light
linker generates bytecode for this custom runtime system. The bytecode is
appended to the end of the custom runtime system, so that it will be
automatically executed when the output file (custom runtime + bytecode) is
launched.
To link in ``custom runtime'' mode, execute the camlc command with:
- the -custom option
- the names of the desired Caml Light object files (.zo files)
- the names of the C object files and libraries (.o and .a files) that
implement the required primitives. (Libraries can also be specified with
the usual -l syntax.)
12.2 The value type
All Caml Light objects are represented by the C type value, defined in the
include file mlvalues.h, along with macros to manipulate values of that type.
An object of type value is either:
- an unboxed integer
- a pointer to a block inside the heap (such as the blocks allocated
through one of the alloc_* functions below)
- a pointer to an object outside the heap (e.g., a pointer to a block
allocated by malloc, or to a C variable).
Chapter 12. Interfacing C with Caml Light 116
12.2.1 Integer values
Integer values encode 31-bit signed integers. They are unboxed (unallocated).
12.2.2 Blocks
Blocks in the heap are garbage-collected, and therefore have strict structure
constraints. Each block includes a header containing the size of the block
(in words), and the tag of the block. The tag governs how the contents of the
blocks are structured. A tag lower than No_scan_tag indicates a structured
block, containing well-formed values, which is recursively traversed by the
garbage collector. A tag greater than or equal to No_scan_tag indicates a raw
block, whose contents are not scanned by the garbage collector. For the
benefits of ad-hoc polymorphic primitives such as equality and structured
input-output, structured and raw blocks are further classified according to
their tags as follows:
---------------------------------------------------------------------
|Tag |Contents of the block |
---------------------------------------------------------------------
|0 to No_scan_tag- 1 |A structured block (an array of Caml Light |
| |objects). Each field is a value. |
|Closure_tag |A closure representing a functional value. |
| |The first word is a pointer to a piece |
| |of bytecode, the second word is a value |
| |containing the environment. |
|String_tag |A character string. |
|Double_tag |A double-precision floating-point number. |
|Abstract_tag |A block representing an abstract datatype. |
|Final_tag |A block representing an abstract datatype with |
| |a ``finalization'' function, to be called when |
| |the block is deallocated. |
---------------------------------------------------------------------
12.2.3 Pointers to outside the heap
Any pointer to outside the heap can be safely cast to and from the type value.
This includes pointers returned by malloc, and pointers to C variables
obtained with the & operator.
12.3 Representation of Caml Light data types
This section describes how Caml Light data types are encoded in the value
type.
12.3.1 Atomic types
int Unboxed integer values.
char Unboxed integer values (ASCII code).
float Blocks with tag Double_tag.
string Blocks with tag String_tag.
12.3.2 Product types
Tuples and arrays are represented by pointers to blocks, with tag 0.
Records are also represented by zero-tagged blocks. The ordering of labels
in the record type declaration determines the layout of the record fields:
the value associated to the label declared first is stored in field 0 of the
block, the value associated to the label declared next goes in field 1, and so
on.
Chapter 12. Interfacing C with Caml Light 117
12.3.3 Concrete types
Constructed terms are represented by blocks whose tag encode the constructor.
The constructors for a given concrete type are numbered from 0 to the number
of constructors minus one, following the order in which they appear in the
concrete type declaration. Constant constructors are represented by
zero-sized blocks (atoms), tagged with the constructor number. Non-constant
constructors declared with a n-tuple as argument are represented by a block of
size n, tagged with the constructor number; the n fields contain the
components of its tuple argument. Other non-constant constructors are
represented by a block of size 1, tagged with the constructor number; the
field 0 contains the value of the constructor argument. Example:
------------------------------------------------------------------------
|Constructed term|Representation |
------------------------------------------------------------------------
|() |Size = 0, tag = 0 |
|false |Size = 0, tag = 0 |
|true |Size = 0, tag = 1 |
|[] |Size = 0, tag = 0 |
|h::t |Size = 2, tag = 1, first field = h, second field = t |
------------------------------------------------------------------------
12.4 Operations on values
12.4.1 Kind tests
- Is_int(v) is true if value v is an immediate integer, false otherwise
- Is_block(v) is true if value v is a pointer to a block, and false if it
is an immediate integer.
12.4.2 Operations on integers
- Val_long(l) returns the value encoding the long int l
- Long_val(v) returns the long int encoded in value v
- Val_int(i) returns the value encoding the int i
- Int_val(v) returns the int encoded in value v
12.4.3 Accessing blocks
- Wosize_val(v) returns the size of value v, in words, excluding the
header.
- Tag_val(v) returns the tag of value v.
th
- Field(v,n) returns the value contained in the n field of the structured
block v. Fields are numbered from 0 to Wosize_val(v)-1.
- Code_val(v) returns the code part of the closure v.
- Env_val(v) returns the environment part of the closure v.
- string_length(v) returns the length (number of characters) of the string
v.
Chapter 12. Interfacing C with Caml Light 118
th
- Byte(v,n) returns the n character of the string v, with type char.
Characters are numbered from 0 to string_length(v)-1.
th
- Byte_u(v,n) returns the n character of the string v, with type unsigned
char. Characters are numbered from 0 to string_length(v)-1.
- String_val(v) returns a pointer to the first byte of the string v, with
type char *. This pointer is a valid C string: there is a null
character after the last character in the string. However, Caml Light
strings can contain embedded null characters, that will confuse the usual
C functions over strings.
- Double_val(v) returns the floating-point number contained in value v,
with type double.
The expressions Field(v,n), Code_val(v), Env_val(v), Byte(v,n), Byte_u(v,n)
and Double_val(v) are valid l-values. Hence, they can be assigned to,
resulting in an in-place modification of value v. Assigning directly to
Field(v,n) must be done with care to avoid confusing the garbage collector
(see below).
12.4.4 Allocating blocks
From the standpoint of the allocation functions, blocks are divided according
to their size as zero-sized blocks, small blocks (with size less than or equal
to Max_young_size), and large blocks (with size greater than to
Max_young_size). The constant Max_young_size is declared in the include file
mlvalues.h. It is guaranteed to be at least 64 (words), so that any block
with constant size less than or equal to 64 can be assumed to be small. For
blocks whose size is computed at run-time, the size must be compared against
Max_young_size to determine the correct allocation procedure.
- Atom(t) returns an ``atom'' (zero-sized block) with tag t. Zero-sized
blocks are preallocated outside of the heap. It is incorrect to try and
allocate a zero-sized block using the functions below. For instance,
Atom(0) represents (), false and []; Atom(1) represents true. (As a
convenience, mlvalues.h defines the macros Val_unit, Val_false and
Val_true.)
- alloc(n,t) returns a fresh small block of size n< Max_young_size words,
with tag t. If this block is a structured block (i.e. if
t<No_scan_tag), then the fields of the block (initially containing
garbage) must be initialized with legal values (using direct assignment
to the fields of the block) before the next allocation.
- alloc_tuple(n) returns a fresh small block of size n<Max_young_size
words, with tag 0. The fields of this block must be filled with legal
values before the next allocation or modification.
- alloc_shr(n,t) returns a fresh block of size n, with tag t. The size of
the block can be greater than Max_young_size. (It can also be smaller,
but in this case it is more efficient to call alloc instead of
alloc_shr.) If this block is a structured block (i.e. if
t<No_scan_tag), then the fields of the block (initially containing
garbage) must be initialized with legal values (using the initialize
function described below) before the next allocation.
Chapter 12. Interfacing C with Caml Light 119
- alloc_string(n) returns a string value of length n characters. The
string initially contains garbage.
- copy_string(s) returns a string value containing a copy of the
null-terminated C string s (a char *).
- copy_double(d) returns a floating-point value initialized with the double
d.
- alloc_array(f,a) allocates an array of values, calling function f over
each element of the input array a to transform it into a value. The
array a is an array of pointers terminated by the null pointer. The
function f receives each pointer as argument, and returns a value. The
zero-tagged block returned by alloc_array(f,a) is filled with the values
returned by the successive calls to f.
- copy_string_array(p) allocates an array of strings, copied from the
pointer to a string array p (a char **).
12.4.5 Raising exceptions
C functions cannot raise arbitrary exceptions. However, two functions are
provided to raise two standard exceptions:
- failwith(s), where s is a null-terminated C string (with type char *),
raises exception Failure with argument s.
- invalid_argument(s), where s is a null-terminated C string (with type
char *), raises exception Invalid_argument with argument s.
12.5 Living in harmony with the garbage collector
Unused blocks in the heap are automatically reclaimed by the garbage
collector. This requires some cooperation from C code that manipulates
heap-allocated blocks.
Rule 1 After a structured block (a block with tag less than No_scan_tag) is
allocated, all fields of this block must be filled with well-formed values
before the next allocation operation. If the block has been allocated with
alloc or alloc_tuple, filling is performed by direct assignment to the fields
of the block:
Field(v,n) =vn;
If the block has been allocated with alloc_shr, filling is performed through
the initialize function:
initialize(&Field(v,n),vn);
The next allocation can trigger a garbage collection. The garbage collector
assumes that all structured blocks contain well-formed values. Newly created
blocks contain random data, which generally do not represent well-formed
values.
If you really need to allocate before the fields can receive their final
value, first initialize with a constant value (e.g. Val_long(0)), then
allocate, then modify the fields with the correct value (see rule 3).
Chapter 12. Interfacing C with Caml Light 120
Rule 2 Local variables containing values must be registered with the garbage
collector (using the Push_roots and Pop_roots macros), if they are to survive
a call to an allocation function.
Registration is performed with the Push_roots and Pop_roots macros.
Push_roots(r,n) declares an array r of n values and registers them with the
garbage collector. The values contained in r[0] to r[n-1] are treated like
roots by the garbage collector. A root value has the following properties:
if it points to a heap-allocated block, this block (and its contents) will not
be reclaimed; moreover, if this block is relocated by the garbage collector,
the root value is updated to point to the new location for the block.
Push_roots(r,n) must occur in a C block exactly between the last local
variable declaration and the first statement in the block. To un-register the
roots, Pop_roots() must be called before the C block containing
Push_roots(r,n) is exited. (Roots are automatically un-registered if a Caml
exception is raised.)
Rule 3 Direct assignment to a field of a block, as in
Field(v,n) =v';
is safe only if v is a block newly allocated by alloc or alloc_tuple; that is,
if no allocation took place between the allocation of v and the assignment to
the field. In all other cases, never assign directly. If the block has just
been allocated by alloc_shr, use initialize to assign a value to a field for
the first time:
'
initialize(&Field(v,n), v);
Otherwise, you are updating a field that previously contained a well-formed
value; then, call the modify function:
'
modify(&Field(v,n), v);
To illustrate the rules above, here is a C function that builds and returns
a list containing the two integers given as parameters:
value alloc_list_int(i1, i2)
int i1, i2;
{
value result;
Push_roots(r, 1);
r[0] = alloc(2, 1); /* Allocate a cons cell */
Field(r[0], 0) = Val_int(i2); /* car = the integer i2 */
Field(r[0], 1) = Atom(0); /* cdr = the empty list [] */
result = alloc(2, 1); /* Allocate the other cons cell */
Field(result, 0) = Val_int(i1); /* car = the integer i1 */
Field(result, 1) = r[0]; /* cdr = the first cons cell */
Pop_roots();
return result;
}
The ``cons'' cell allocated first needs to survive the allocation of the other
cons cell; hence, the value returned by the first call to alloc must be stored
in a registered root. The value returned by the second call to alloc can
reside in the un-registered local variable result, since we won't do any
further allocation in this function.
Chapter 12. Interfacing C with Caml Light 121
In the example above, the list is built bottom-up. Here is an alternate
way, that proceeds top-down. It is less efficient, but illustrates the use of
modify.
value alloc_list_int(i1, i2)
int i1, i2;
{
value tail;
Push_roots(r, 1);
r[0] = alloc(2, 1); /* Allocate a cons cell */
Field(r[0], 0) = Val_int(i1); /* car = the integer i1 */
Field(r[0], 1) = Val_int(0); /* A dummy value
tail = alloc(2, 1); /* Allocate the other cons cell */
Field(tail, 0) = Val_int(i2); /* car = the integer i2 */
Field(tail, 1) = Atom(0); /* cdr = the empty list [] */
modify(&Field(r[0], 1), tail); /* cdr of the result = tail */
Pop_roots();
return r[0];
}
It would be incorrect to perform Field(r[0], 1) = tail directly, because the
allocation of tail has taken place since r[0] was allocated.
12.6 A complete example
This section outlines how the functions from the Unix curses library can be
made available to Caml Light programs. First of all, here is the interface
curses.mli that declares the curses primitives and data types:
type window;; (* The type "window" remains abstract *)
value initscr: unit -> window = 1 "curses_initscr"
and endwin: unit -> unit = 1 "curses_endwin"
and refresh: unit -> unit = 1 "curses_refresh"
and wrefresh : window -> unit = 1 "curses_wrefresh"
and newwin: int -> int -> int -> int -> window = 4 "curses_newwin"
and mvwin: window -> int -> int -> unit = 3 "curses_mvwin"
and addch: char -> unit = 1 "curses_addch"
and mvwaddch: window -> int -> int -> char -> unit = 4 "curses_mvwaddch"
and addstr: string -> unit = 1 "curses_addstr"
and mvwaddstr: window -> int -> int -> string -> unit = 4 "curses_mvwaddstr"
;; (* lots more omitted *)
To compile this interface:
camlc -c curses.mli
To implement these functions, we just have to provide the stub code; the
core functions are already implemented in the curses library. The stub code
file, curses.o, looks like:
#include <curses.h>
#include <mlvalues.h>
value curses_initscr(unit)
value unit;
{
Chapter 12. Interfacing C with Caml Light 122
return (value) initscr(); /* OK to coerce directly from WIN-
DOW * to value
since that's a block created by malloc() */
}
value curses_wrefresh(win)
value win;
{
wrefresh((value) win);
return Val_unit; /* Or Atom(0) */
}
value curses_newwin(nlines, ncols, x0, y0)
value nlines, ncols, x0, y0;
{
return (value) newwin(Int_val(nlines), Int_val(ncols),
Int_val(x0), Int_val(y0));
}
value curses_addch(c)
value c;
{
addch(Int_val(c)); /* Characters are encoded like integers */
return Val_unit;
}
value curses_addstr(s)
value s;
{
addstr(String_val(s));
return Val_unit;
}
/* This goes on for pages. */
(Actually, it would be better to create a library for the stub code, with each
stub code function in a separate file, so that linking would pick only those
functions from the curses library that are actually used.)
The file curses.c can be compiled with:
cc -c -I/usr/local/lib/caml-light curses.c
or, even simpler,
camlc -c curses.c
(When passed a .c file, the camlc command simply calls cc on that file, with
the right -I option.)
Now, here is a sample Caml Light program test.ml that uses the curses
module:
#open "curses";;
let main_window = initscr () in
let small_window = newwin 10 5 20 10 in
mvwaddstr main_window 10 2 "Hello";
mvwaddstr small_window 4 3 "world";
refresh();
for i = 1 to 100000 do () done;
Chapter 12. Interfacing C with Caml Light 123
endwin()
;;
To compile this program, run:
camlc -c test.ml
Finally, to link everything together:
camlc -custom -o test test.zo curses.o -lcurses
Part V
Appendix
124
Chapter 13
Further reading
For the interested reader, we list below some references to books and reports
related (sometimes loosely) to Caml Light.
13.1 Programming in ML
The books below are programming courses taught in ML. Their main goal is to
teach programming, not to describe ML in full details --- though most contain
fairly good introductions to the ML language. Some of those books use the
Standard ML dialect instead of the Caml dialect, so you will have to keep in
mind the differences in syntax and in semantics.
- Pierre Weis and Xavier Leroy. Le langage Caml. InterEditions, 1993.
The natural companion to this manual, provided you read French. This
book is a step-by-step introduction to programming in Caml, and presents
many realistic examples of Caml programs.
- Lawrence C. Paulson. ML for the working programmer. Cambridge
University Press, 1991.
An excellent introduction to programming in Standard ML. Develops a
theorem prover as a complete example. Contains a presentation of the
module system of Standard ML.
- Chris Reade. Elements of Functional Programming. Addison-Wesley, 1989.
An introduction to Standard ML, with sections on denotational semantics
and lambda-calculus.
- Ryan Stansifer. ML primer. Prentice-Hall, 1992.
A short, but nice introduction to programming in Standard ML.
- Therese Accart Hardin and Veronique Donzeau-Gouge Viguie. Concepts et
outils de la programmation. Du fonctionnel a l'imperatif avec Caml et
Ada. InterEditions, 1992.
A first course in programming, that first introduces the main programming
notions in Caml, then shows them underlying Ada. Intended for beginners;
slow-paced for the others.
125
Chapter 13. Further reading 126
- Ake Wikstrom. Functional programming using Standard ML. Prentice-Hall,
1987.
A first course in programming, taught in Standard ML. Intended for
absolute beginners; slow-paced for the others.
- Harold Abelson and Gerald Jay Sussman. Structure and Interpretation of
Computer Programs. The MIT press, 1985. (French translation: Structure
et interpretation des programmes informatiques, InterEditions, 1989.)
An outstanding course on programming, taught in Scheme, the modern
dialect of Lisp. Well worth reading, even if you are more interested in
ML than in Lisp.
13.2 Descriptions of ML dialects
The books and reports below are descriptions of various programming languages
from the ML family. They assume some familiarity with ML.
- Xavier Leroy and Pierre Weis. Manuel de reference du langage Caml.
InterEditions, 1993.
The French edition of the present reference manual and user's manual.
- Robert Harper. Introduction to Standard ML. Technical report
ECS-LFCS-86-14, University of Edinburgh, 1986.
An overview of Standard ML, including the module system. Terse, but
still readable.
- Robin Milner, Mads Tofte and Robert Harper. The definition of Standard
ML. The MIT press, 1990.
A complete formal definition of Standard ML, in the framework of
structured operational semantics. This book is probably the most
mathematically precise definition of a programming language ever written.
It is heavy on formalism and horribly terse, so even readers that are
thoroughly familiar with ML will have major difficulties with it.
- Robin Milner and Mads Tofte. Commentary on Standard ML. The MIT Press,
1991.
A commentary on the book above, that attempts to explain the most
delicate parts and motivate the design choices. Easier to read than the
Definition, but still rather involving.
- Guy Cousineau and Gerard Huet. The CAML primer. Technical report 122,
INRIA, 1990.
A short description of the original Caml system, from which Caml Light
has evolved. Some familiarity with Lisp is assumed.
- Pierre Weis et al. The CAML reference manual, version 2.6.1. Technical
report 121, INRIA, 1990.
The manual for the original Caml system, from which Caml Light has
evolved.
Chapter 13. Further reading 127
- Michael J. Gordon, Arthur J. Milner and Christopher P. Wadsworth.
Edinburgh LCF. Lecture Notes in Computer Science volume 78,
Springer-Verlag, 1979.
This is the first published description of the ML language, at the time
when it was nothing more than the control language for the LCF system, a
theorem prover. This book is now obsolete, since the ML language has
much evolved since then; but it is still of historical interest.
- Paul Hudak, Simon Peyton-Jones and Philip Wadler. Report on the
programming language Haskell, version 1.1. Technical report, Yale
University, 1991.
Haskell is a purely functional language with lazy semantics that shares
many important points with ML (full functionality, polymorphic typing),
but has interesting features of its own (dynamic overloading, also called
type classes).
13.3 Implementing functional programming languages
The references below are intended for those who are curious to learn how
a language like Caml Light is compiled and implemented.
- Xavier Leroy. The ZINC experiment: an economical implementation of the
ML language. Technical report 117, INRIA, 1990. (Available by anonymous
FTP on ftp.inria.fr.)
A description of the ZINC implementation, the prototype ML implementation
that has evolved into Caml Light. Large parts of this report still apply
to the current Caml Light system, in particular the description of the
execution model and abstract machine. Other parts are now obsolete. Yet
this report still gives a complete overview of the implementation
techniques used in Caml Light.
- Simon Peyton-Jones. The implementation of functional programming
languages. Prentice-Hall, 1987. (French translation: Mise en uvre des
langages fonctionnels de programmation, Masson, 1990.)
An excellent description of the implementation of purely functional
languages with lazy semantics, using the technique known as graph
reduction. The part of the book that deals with the transformation from
ML to enriched lambda-calculus directly applies to Caml Light. You will
find a good description of how pattern-matching is compiled and how types
are inferred. The remainder of the book does not apply directly to Caml
Light, since Caml Light is not purely functional (it has side-effects),
has strict semantics, and does not use graph reduction at all.
- Andrew W. Appel. Compiling with continuations. Cambridge University
Press, 1992.
A complete description of an optimizing compiler for Standard ML, based
on an intermediate representation called continuation-passing style.
Shows how many advanced program optimizations can be applied to ML. Not
directly relevant to the Caml Light system, since Caml Light does not use
continuation-passing style at all, and makes little attempts at
Chapter 13. Further reading 128
optimizing programs.
13.4 Applications of ML
The following reports show ML at work in various, sometimes unexpected, areas.
- Emmanuel Chailloux and Guy Cousineau. The MLgraph primer. Technical
report 92-15, Ecole Normale Superieure, 1992. (Available by anonymous
FTP on ftp.ens.fr.)
Describes a Caml Light library that produces Postscript pictures through
high-level drawing functions.
- Xavier Leroy. Programmation du systeme Unix en Caml Light. Technical
report 147, INRIA, 1992. (Available by anonymous FTP on ftp.inria.fr.)
A Unix systems programming course, demonstrating the use of the Caml
Light library that gives access to Unix system calls.
- John H. Reppy. Concurrent programming with events --- The concurrent ML
manual. Cornell University, 1990. (Available by anonymous FTP on
research.att.com.)
Concurrent ML extends Standard ML of New Jersey with concurrent processes
that communicate through channels and events.
- Jeannette M. Wing, Manuel Faehndrich, J. Gregory Morrisett and Scottt
Nettles. Extensions to Standard ML to support transactions. Technical
report CMU-CS-92-132, Carnegie-Mellon University, 1992. (Available by
anonymous FTP on reports.adm.cs.cmu.edu.)
How to integrate the basic database operations to Standard ML.
- Emden R. Gansner and John H. Reppy. eXene. Bell Labs, 1991. (Available
by anonymous FTP on research.att.com.)
An interface between Standard ML of New Jersey and the X Windows
windowing system.
Index to the library
! (infix), 56 Break (exception), 75
!= (infix), 42 builtin (module), 41
* (infix), 44, 46 button_down, 82
*. (infix), 44 catch_break, 75
+ (infix), 43, 45 cd, 95
+. (infix), 43 char (module), 41
- (infix), 44, 46 char_for_read, 42
-. (infix), 44 char_of_int, 41
/ (infix), 44, 46 chdir, 75
/. (infix), 44 check_suffix, 64
< (infix), 44, 46 chop_suffix, 64
<. (infix), 44 clear, 65, 70, 73
<= (infix), 44, 46 clear_graph, 78
<=. (infix), 44 clear_parser, 69
<> (infix), 42 close, 74
<>. (infix), 44 close_graph, 78
= (infix), 42 close_in, 53
=. (infix), 44 close_out, 51
== (infix), 42 combine, 55
> (infix), 44, 46 command_line, 73
>. (infix), 44 compare, 63, 72
>= (infix), 44, 46 compare_strings, 58
>=. (infix), 44 compile, 95
@ (infix), 53 concat, 63
^ (infix), 57 concat_vect, 59
abs, 46 contains, 62
abs_float, 45 copy_vect, 59
acos, 44 cos, 44
add, 62, 65, 68, 70, 71 create_image, 81
add_float, 43 create_lexer, 67
add_int, 45 create_lexer_channel, 66
arg (module), 61 create_lexer_string, 67
asin, 44 create_string, 58
asr (infix), 47 current_dir_name, 63
assoc, 55 current_point, 79
assq, 55 cyan, 79
atan, 44 debug_mode, 95
atan2, 44 decr, 56
background, 79 diff, 72
Bad (exception), 62 dirname, 64
baltree (module), 62 div_float, 44
basename, 64 div_int, 46
black, 79 Division_by_zero (exception), 45
blit_image, 81 do_list, 53
blit_string, 58 do_list2, 53
blit_vect, 60 do_list_combine, 56
blue, 79 do_stream, 57
bool (module), 40 do_table, 66
129
Index to the library 130
do_vect, 60 ge_string, 58
draw_arc, 79 genlex (module), 64
draw_char, 80 get_image, 81
draw_circle, 80 get_lexeme, 67
draw_ellipse, 79 get_lexeme_char, 67
draw_image, 81 get_lexeme_end, 67
draw_string, 80 get_lexeme_start, 67
dump_image, 81 getenv, 75
elements, 72 Graphic_failure (exception), 78
empty, 68, 71 graphics (module), 78
Empty (exception), 70, 73 green, 79
End_of_file (exception), 48 gt_float, 44
end_of_stream, 57 gt_int, 46
eq (module), 42 gt_string, 58
eq_float, 44 hash, 66
eq_int, 46 hash_param, 66
eq_string, 58 hashtbl (module), 65
equal, 72 hd, 53
exc (module), 42 in_channel_length, 52
except, 54 include, 94
exceptq, 54 incr, 56
exists, 54 index, 55
exit, 48, 74 init, 71
Exit (exception), 43 input, 52
exp, 44 input_binary_int, 52
Failure (exception), 43 input_byte, 52
failwith, 43 input_char, 51
fchar (module), 43 input_line, 51
filename (module), 63 input_value, 52
fill_arc, 80 int, 71
fill_circle, 81 int (module), 45
fill_ellipse, 80 int_of_char, 41
fill_poly, 80 int_of_float, 43
fill_rect, 80 int_of_string, 47
fill_string, 58 inter, 72
fill_vect, 60 interactive, 74
find, 63, 65, 68 intersect, 55
find_all, 65 invalid_arg, 43
flat_map, 54 Invalid_argument (exception), 42
float, 71 io (module), 47
float (module), 43 is_absolute, 64
float_of_int, 43 is_empty, 71
float_of_string, 45 it_list, 53
flush, 50 it_list2, 54
fold, 72 iter, 68, 71--73
for_all, 54 key_pressed, 82
foreground, 79
fprint, 70 land (infix), 47
fprintf, 69 le_float, 44
fst, 55 le_int, 46
fstring (module), 45 le_string, 58
fvect (module), 45 length, 70, 73
gc, 95 lexing (module), 66
ge_float, 44 lineto, 79
ge_int, 46 list (module), 53
list_it, 53
Index to the library 131
list_it2, 54 open_graph, 78
list_length, 53 open_in, 51
list_of_vect, 60 open_in_bin, 51
lnot, 47 open_in_gen, 51
load, 94 open_out, 49
load_object, 95 open_out_bin, 49
log, 44 open_out_gen, 50
lor (infix), 47 out_channel_length, 51
lshift_left, 47 Out_of_memory (exception), 42
lshift_right, 47 output, 50
lsl (infix), 47 output_binary_int, 50
lsr (infix), 47 output_byte, 50
lt_float, 44 output_char, 50
lt_int, 46 output_string, 50
lt_string, 58 output_value, 50
lxor (infix), 47 pair (module), 55
magenta, 79 parse, 62
make_image, 81 Parse_error (exception), 56
make_lexer, 64 Parse_failure (exception), 56
make_matrix, 59 parsing (module), 68
make_string, 58 peek, 70
make_vect, 59 plot, 79
map, 53 point_color, 79
map (module), 67 pop, 73
map2, 53 pos_in, 52
map_combine, 55 pos_out, 51
map_vect, 60 power, 44
map_vect_list, 60 pred, 45
Match_failure (exception), 26, 28, prerr_char, 48
41 prerr_endline, 49
max, 46 prerr_float, 49
mem, 54, 71 prerr_int, 49
mem_assoc, 55 prerr_string, 49
memq, 54 print, 70
merge, 72 print_char, 48
min, 46 print_endline, 48
minus, 43, 45 print_float, 48
minus_float, 43 print_int, 48
minus_int, 45 print_newline, 48
mod (infix), 46 print_string, 48
modify, 63 printexc (module), 69
mouse_pos, 82 printf, 70
moveto, 79 printf (module), 69
mult_float, 44 push, 73
mult_int, 46 queue (module), 70
neq_float, 44 quit, 94
neq_int, 46 quo (infix), 46
neq_string, 58 raise, 42
new, 65, 70, 73 random (module), 71
not (infix), 41 read_float, 49
Not_found (exception), 43 read_int, 49
nth_char, 57 read_key, 82
open, 74 read_line, 49
open_descriptor_in, 51 really_input, 52
open_descriptor_out, 50 red, 79
Index to the library 132
ref (module), 56 string_of_int, 47
remove, 63, 66, 68, 72, 74 sub_float, 44
rename, 75 sub_int, 46
replace_string, 58 sub_string, 58
rev, 53 sub_vect, 59
rgb, 78 subtract, 54
rhs_end, 68 succ, 45
rhs_start, 68 symbol_end, 68
s_irall, 74 symbol_start, 68
s_irgrp, 74 sys (module), 73
s_iroth, 74 Sys_error (exception), 73
s_irusr, 74 take, 70
s_isgid, 74 tan, 44
s_isuid, 74 text_size, 80
s_iwall, 74 tl, 53
s_iwgrp, 74 trace, 95
s_iwoth, 74 transp, 81
s_iwusr, 74 union, 54, 72
s_ixall, 74 untrace, 95
s_ixgrp, 74
s_ixoth, 74 vect (module), 59
s_ixusr, 74 vect_assign, 59
seek_in, 52 vect_item, 59
seek_out, 50 vect_length, 59
set (module), 71 vect_of_list, 60
set_color, 79 verbose_mode, 95
set_font, 80
set_line_width, 80 wait_next_event, 82
set_nth_char, 57 white, 79
set_text_size, 80
sin, 44 yellow, 79
size_x, 78
size_y, 78
snd, 55
sort, 72
sort (module), 72
sound, 82
split, 55, 63
sqrt, 44
stack (module), 73
std_err, 48
std_in, 48
std_out, 48
stderr, 48
stdin, 48
stdout, 48
stream (module), 56
stream_check, 57
stream_from, 56
stream_get, 57
stream_next, 56
stream_of_channel, 57
stream_of_string, 57
string (module), 57
string_for_read, 59
string_length, 57
string_of_float, 45
Index of keywords
and, see let, type, exception, value
begin, 24, 25
do, see while, for
done, see while, for
downto, see for
else, see if
end, 24, 25
exception, see also 42, 33, 34
for, 24, 28
fun, 24
function, 24
if, 24, 27
in, see let
let, 24, 26
match, 24, 27
mutable, 32
not, 24
of, see type, exception
or, 24, 28
prefix, 24, 30
rec, see let
then, see if
to, see for
try, 24, 28
type, 32, 34
value, 34
while, 28
with, see match, try
133