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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html> <html>
<head> <head>
<title>SWIG and Ocaml</title> <title>SWIG and Ocaml</title>
<link rel="stylesheet" type="text/css" href="style.css"> <link rel="stylesheet" type="text/css" href="style.css">
</head> </head>
<body bgcolor="#ffffff">
<a name="n1"></a> <body bgcolor="#ffffff">
<H1><a name="Ocaml"></a>31 SWIG and Ocaml</H1> <H1><a name="Ocaml"></a>31 SWIG and Ocaml</H1>
<!-- INDEX --> <!-- INDEX -->
<div class="sectiontoc"> <div class="sectiontoc">
@ -59,20 +59,23 @@
<p> <p>
This chapter describes SWIG's This chapter describes SWIG's support of Ocaml.
support of Ocaml. Ocaml is a relatively recent addition to the ML family, </p>
and is a recent addition to SWIG. It's the second compiled, typed
language to be added. Ocaml has widely acknowledged benefits for engineers, <p>
mostly derived from a sophisticated type system, compile-time checking Ocaml is a relatively recent addition to the ML family,
which eliminates several classes of common programming errors, and good and is a recent addition to SWIG. It's the second compiled, typed
native performance. While all of this is wonderful, there are well-written language to be added. Ocaml has widely acknowledged benefits for engineers,
C and C++ libraries that Ocaml users will want to take advantage of as mostly derived from a sophisticated type system, compile-time checking
part of their arsenal (such as SSL and gdbm), as well as their own mature which eliminates several classes of common programming errors, and good
C and C++ code. SWIG allows this code to be used in a natural, type-safe native performance. While all of this is wonderful, there are well-written
way with Ocaml, by providing the necessary, but repetitive glue code C and C++ libraries that Ocaml users will want to take advantage of as
which creates and uses Ocaml values to communicate with C and C++ code. part of their arsenal (such as SSL and gdbm), as well as their own mature
In addition, SWIG also produces the needed Ocaml source that binds C and C++ code. SWIG allows this code to be used in a natural, type-safe
variants, functions, classes, etc. way with Ocaml, by providing the necessary, but repetitive glue code
which creates and uses Ocaml values to communicate with C and C++ code.
In addition, SWIG also produces the needed Ocaml source that binds
variants, functions, classes, etc.
</p> </p>
<p> <p>
@ -84,17 +87,16 @@ If you're not familiar with the Objective Caml language, you can visit
<p> <p>
SWIG 3.0 works with Ocaml 3.08.3 and above. Given the choice, SWIG 3.0 works with Ocaml 3.08.3 and above. Given the choice,
you should use the latest stable release. The SWIG Ocaml module has you should use the latest stable release. The SWIG Ocaml module has
been tested on Linux (x86,PPC,Sparc) and Cygwin on Windows. The been tested on Linux (x86,PPC,Sparc) and Cygwin on Windows. The
best way to determine whether your system will work is to compile the best way to determine whether your system will work is to compile the
examples and test-suite which come with SWIG. You can do this by running examples and test-suite which come with SWIG. You can do this by running
<tt>make check</tt> from the SWIG root directory after installing SWIG. <tt>make check</tt> from the SWIG root directory after installing SWIG.
The Ocaml module has been tested using the system's dynamic linking (the The Ocaml module has been tested using the system's dynamic linking (the
usual -lxxx against libxxx.so, as well as with Gerd Stolpmann's usual -lxxx against libxxx.so, as well as with Gerd Stolpmann's
<a <a href="http://download.camlcity.org/download/">Dl package</a>.
href="http://download.camlcity.org/download/">Dl package The ocaml_dynamic and ocaml_dynamic_cpp targets in the
</a>. The ocaml_dynamic and ocaml_dynamic_cpp targets in the
file Examples/Makefile illustrate how to compile and link SWIG modules that file Examples/Makefile illustrate how to compile and link SWIG modules that
will be loaded dynamically. This has only been tested on Linux so far. will be loaded dynamically. This has only been tested on Linux so far.
</p> </p>
@ -103,24 +105,24 @@ will be loaded dynamically. This has only been tested on Linux so far.
<p> <p>
The basics of getting a SWIG Ocaml module up and running The basics of getting a SWIG Ocaml module up and running
can be seen from one of SWIG's example Makefiles, but is also described can be seen from one of SWIG's example Makefiles, but is also described
here. To build an Ocaml module, run SWIG using the <tt>-ocaml</tt> here. To build an Ocaml module, run SWIG using the <tt>-ocaml</tt>
option. option.
</p> </p>
<div class="code"> <div class="code">
<pre> <pre>
%swig -ocaml example.i %swig -ocaml example.i
</pre> </pre>
</div> </div>
<p> This will produce 3 files. The file <tt>example_wrap.c</tt> contains <p>This will produce 3 files. The file <tt>example_wrap.c</tt> contains
all of the C code needed to build an Ocaml module. To build the module, all of the C code needed to build an Ocaml module. To build the module,
you will compile the file <tt>example_wrap.c</tt> with <tt>ocamlc</tt> or you will compile the file <tt>example_wrap.c</tt> with <tt>ocamlc</tt> or
<tt>ocamlopt</tt> to create the needed .o file. You will need to compile <tt>ocamlopt</tt> to create the needed .o file. You will need to compile
the resulting .ml and .mli files as well, and do the final link with -custom the resulting .ml and .mli files as well, and do the final link with -custom
(not needed for native link). </p> (not needed for native link).</p>
<H3><a name="Ocaml_nn4"></a>31.1.2 Compiling the code</H3> <H3><a name="Ocaml_nn4"></a>31.1.2 Compiling the code</H3>
@ -134,28 +136,29 @@ the type of each SWIG'ed module's c_obj is derived from Swig.c_obj_t. This
also allows SWIG to acquire new conversions painlessly, as well as giving also allows SWIG to acquire new conversions painlessly, as well as giving
the user more freedom with respect to custom typing. the user more freedom with respect to custom typing.
Use <tt>ocamlc</tt> or <tt>ocamlopt</tt> to compile your Use <tt>ocamlc</tt> or <tt>ocamlopt</tt> to compile your SWIG interface like:
SWIG interface like:
</p> </p>
<div class="code"> <div class="code">
<pre> <pre>
% swig -ocaml -co swig.mli ; swig -ocaml co swig.ml % swig -ocaml -co swig.mli ; swig -ocaml co swig.ml
% ocamlc -c swig.mli ; ocamlc -c swig.ml % ocamlc -c swig.mli ; ocamlc -c swig.ml
% ocamlc -c -ccopt "-I/usr/include/foo" example_wrap.c % ocamlc -c -ccopt "-I/usr/include/foo" example_wrap.c
% ocamlc -c example.mli % ocamlc -c example.mli
% ocamlc -c example.ml % ocamlc -c example.ml
</pre> </pre>
</div> </div>
<p> <tt>ocamlc</tt> is aware of .c files and knows how to handle them. Unfortunately, <p><tt>ocamlc</tt> is aware of .c files and knows how to handle them. Unfortunately,
it does not know about .cxx, .cc, or .cpp files, so when SWIG is invoked it does not know about .cxx, .cc, or .cpp files, so when SWIG is invoked
in C++ mode, you must: </p> in C++ mode, you must:</p>
<div class="code"> <div class="code">
<pre> <pre>
% cp example_wrap.cxx example_wrap.cxx.c<br>% ocamlc -c ... -ccopt -xc++ example_wrap.cxx.c<br>% ...<br> % cp example_wrap.cxx example_wrap.cxx.c
</pre> % ocamlc -c ... -ccopt -xc++ example_wrap.cxx.c
% ...
</pre>
</div> </div>
<H3><a name="Ocaml_nn5"></a>31.1.3 The camlp4 module</H3> <H3><a name="Ocaml_nn5"></a>31.1.3 The camlp4 module</H3>
@ -244,8 +247,8 @@ toplevel ocaml interpreter. Consult the ocaml manual for details.
<p> <p>
When linking any ocaml bytecode with your module, use the -custom When linking any ocaml bytecode with your module, use the -custom
option to build your functions into the primitive list. This option to build your functions into the primitive list. This
option is not needed when you build native code. option is not needed when you build native code.
</p> </p>
<H3><a name="Ocaml_nn7"></a>31.1.5 Compilation problems and compiling with C++</H3> <H3><a name="Ocaml_nn7"></a>31.1.5 Compilation problems and compiling with C++</H3>
@ -273,7 +276,7 @@ In the code as seen by the typemap
writer, there is a value, swig_result, that always contains the writer, there is a value, swig_result, that always contains the
current return data. It is a list, and must be appended with the current return data. It is a list, and must be appended with the
caml_list_append function, or with functions and macros provided by caml_list_append function, or with functions and macros provided by
objective caml.<br> objective caml.
</p> </p>
<div class="code"><pre> <div class="code"><pre>
@ -299,66 +302,65 @@ type c_obj =
</pre></div> </pre></div>
<p> <p>
A few functions exist which generate and return these: A few functions exist which generate and return these:
</p> </p>
<ul> <ul>
<li>caml_ptr_val receives a c_obj and returns a void *. &nbsp;This <li>caml_ptr_val receives a c_obj and returns a void *. This
should be used for all pointer purposes.</li> should be used for all pointer purposes.</li>
<li>caml_long_val receives a c_obj and returns a long. &nbsp;This <li>caml_long_val receives a c_obj and returns a long. This
should be used for most integral purposes.<br> should be used for most integral purposes.</li>
</li> <li>caml_val_ptr receives a void * and returns a c_obj.</li>
<li>caml_val_ptr receives a void * and returns a c_obj.</li> <li>caml_val_bool receives a C int and returns a c_obj representing
<li>caml_val_bool receives a C int and returns a c_obj representing its bool value.</li>
its bool value.</li> <li>caml_val_(u)?(char|short|int|long|float|double) receives an
<li>caml_val_(u)?(char|short|int|long|float|double) receives an appropriate C value and returns a c_obj representing it.</li>
appropriate C value and returns a c_obj representing it.</li> <li>caml_val_string receives a char * and returns a string value.</li>
<li>caml_val_string receives a char * and returns a string value.</li> <li>caml_val_string_len receives a char * and a length and returns
<li>caml_val_string_len receives a char * and a length and returns a string value.</li>
a string value.</li> <li>caml_val_obj receives a void * and an object type and returns
<li>caml_val_obj receives a void * and an object type and returns a C_obj, which contains a closure giving method access.</li>
a C_obj, which contains a closure giving method access.</li>
</ul> </ul>
<p> <p>
Because of this style, a typemap can return any kind of value it Because of this style, a typemap can return any kind of value it
wants from a function. &nbsp;This enables out typemaps and inout typemaps wants from a function. This enables out typemaps and inout typemaps
to work well. &nbsp;The one thing to remember about outputting values to work well. The one thing to remember about outputting values
is that you must append them to the return list with swig_result = caml_list_append(swig_result,v). is that you must append them to the return list with swig_result = caml_list_append(swig_result,v).
</p> </p>
<p> <p>
&nbsp;This function will return a new list that has your element This function will return a new list that has your element
appended. Upon return to caml space, the fnhelper function appended. Upon return to caml space, the fnhelper function
beautifies the result. A list containing a single item degrades to beautifies the result. A list containing a single item degrades to
only that item (i.e. [ C_int 3 ] -&gt; C_int 3), and a list only that item (i.e. [ C_int 3 ] -&gt; C_int 3), and a list
containing more than one item is wrapped in C_list (i.e. [ C_char containing more than one item is wrapped in C_list (i.e. [ C_char
'a' ; C_char 'b' -&gt; C_list [ C_char 'a' ; C_char b 'a' ; C_char 'b' -&gt; C_list [ C_char 'a' ; C_char b
]). &nbsp;This is in order to make return values easier to handle ]). This is in order to make return values easier to handle
when functions have only one return value, such as constructors, when functions have only one return value, such as constructors,
and operators. &nbsp;In addition, string, pointer, and object and operators. In addition, string, pointer, and object
values are interchangeable with respect to caml_ptr_val, so you can values are interchangeable with respect to caml_ptr_val, so you can
allocate memory as caml strings and still use the resulting allocate memory as caml strings and still use the resulting
pointers for C purposes, even using them to construct simple objects pointers for C purposes, even using them to construct simple objects
on. Note, though, that foreign C++ code does not respect the garbage on. Note, though, that foreign C++ code does not respect the garbage
collector, although the SWIG interface does.</p> collector, although the SWIG interface does.</p>
<p> <p>
The wild card type that you can use in lots of different ways is The wild card type that you can use in lots of different ways is
C_obj. It allows you to wrap any type of thing you like as an C_obj. It allows you to wrap any type of thing you like as an
object using the same mechanism that the ocaml module object using the same mechanism that the ocaml module
does. &nbsp;When evaluated in caml_ptr_val, the returned value is does. When evaluated in caml_ptr_val, the returned value is
the result of a call to the object's "&amp;" operator, taken as a pointer. the result of a call to the object's "&amp;" operator, taken as a pointer.
</p> </p>
<p>
You should only construct values using objective caml, or using the <p>
functions caml_val_* functions provided as static functions to a SWIG You should only construct values using objective caml, or using the
ocaml module, as well as the caml_list_* functions. These functions functions caml_val_* functions provided as static functions to a SWIG
provide everything a typemap needs to produce values. In addition, ocaml module, as well as the caml_list_* functions. These functions
value items pass through directly, but you must make your own type provide everything a typemap needs to produce values. In addition,
signature for a function that uses value in this way. value items pass through directly, but you must make your own type
</p> signature for a function that uses value in this way.
</p>
<H3><a name="Ocaml_nn9"></a>31.2.1 The generated module</H3> <H3><a name="Ocaml_nn9"></a>31.2.1 The generated module</H3>
@ -399,11 +401,11 @@ it describes the output SWIG will generate for class definitions.
<p> <p>
SWIG will wrap enumerations as polymorphic variants in the output SWIG will wrap enumerations as polymorphic variants in the output
Ocaml code, as above in C_enum.&nbsp; In order to support all Ocaml code, as above in C_enum. In order to support all
C++-style uses of enums, the function int_to_enum and enum_to_int are C++-style uses of enums, the function int_to_enum and enum_to_int are
provided for ocaml code to produce and consume these values as provided for ocaml code to produce and consume these values as
integers. &nbsp;Other than that, correct uses of enums will not have integers. Other than that, correct uses of enums will not have
a problem. &nbsp;Since enum labels may overlap between enums, the a problem. Since enum labels may overlap between enums, the
enum_to_int and int_to_enum functions take an enum type label as an enum_to_int and int_to_enum functions take an enum type label as an
argument. Example: argument. Example:
</p> </p>
@ -435,14 +437,14 @@ type c_enum_tag = [
val int_to_enum c_enum_type -&gt; int -&gt; c_obj val int_to_enum c_enum_type -&gt; int -&gt; c_obj
val enum_to_int c_enum_type -&gt; c_obj -&gt; c_obj val enum_to_int c_enum_type -&gt; c_obj -&gt; c_obj
</pre> </pre>
</div> </div>
<p> <p>
So it's possible to do this: So it's possible to do this:
</p> </p>
<div class="code"> <div class="code">
<pre> <pre>
bash-2.05a$ ocamlmktop -custom enum_test_wrap.o enum_test.cmo -o enum_test_top bash-2.05a$ ocamlmktop -custom enum_test_wrap.o enum_test.cmo -o enum_test_top
bash-2.05a$ ./enum_test_top bash-2.05a$ ./enum_test_top
Objective Caml version 3.04 Objective Caml version 3.04
@ -455,7 +457,7 @@ val x : Enum_test.c_obj = C_enum `a
# int_to_enum `c_enum_type 4 ;; # int_to_enum `c_enum_type 4 ;;
- : Enum_test.c_obj = C_enum `c - : Enum_test.c_obj = C_enum `c
</pre> </pre>
</div> </div>
<H4><a name="Ocaml_nn11"></a>31.2.2.1 Enum typing in Ocaml</H4> <H4><a name="Ocaml_nn11"></a>31.2.2.1 Enum typing in Ocaml</H4>
@ -577,14 +579,14 @@ void printfloats( float *tab, int len );
<p> <p>
C++ classes, along with structs and unions are represented by C_obj C++ classes, along with structs and unions are represented by C_obj
(string -&gt; c_obj -&gt; c_obj) wrapped closures. &nbsp;These objects (string -&gt; c_obj -&gt; c_obj) wrapped closures. These objects
contain a method list, and a type, which allow them to be used like contain a method list, and a type, which allow them to be used like
C++ objects. When passed into typemaps that use pointers, they C++ objects. When passed into typemaps that use pointers, they
degrade to pointers through their "&amp;" method. &nbsp;Every method degrade to pointers through their "&amp;" method. Every method
an object has is represented as a string in the object's method table, an object has is represented as a string in the object's method table,
and each method table exists in memory only once. &nbsp;In addition and each method table exists in memory only once. In addition
to any other operators an object might have, certain builtin ones are to any other operators an object might have, certain builtin ones are
provided by SWIG: (all of these take no arguments (C_void)) provided by SWIG: (all of these take no arguments (C_void))
</p> </p>
<table summary="SWIG provided operators"> <table summary="SWIG provided operators">
@ -703,7 +705,7 @@ Here's a simple example using Trolltech's Qt Library:
</p> </p>
<table border="1" bgcolor="#dddddd" summary="Qt Library example"> <table border="1" bgcolor="#dddddd" summary="Qt Library example">
<tr><th><center>qt.i</center></th></tr> <tr><th><center>qt.i</center></th></tr>
<tr><td><pre> <tr><td><pre>
%module qt %module qt
%{ %{
@ -733,7 +735,7 @@ bash-2.05a$ QTPATH=/your/qt/path
bash-2.05a$ for file in swig.mli swig.ml swigp4.ml ; do swig -ocaml -co $file ; done bash-2.05a$ for file in swig.mli swig.ml swigp4.ml ; do swig -ocaml -co $file ; done
bash-2.05a$ ocamlc -c swig.mli ; ocamlc -c swig.ml bash-2.05a$ ocamlc -c swig.mli ; ocamlc -c swig.ml
bash-2.05a$ ocamlc -I `camlp4 -where` -pp "camlp4o pa_extend.cmo q_MLast.cmo" -c swigp4.ml bash-2.05a$ ocamlc -I `camlp4 -where` -pp "camlp4o pa_extend.cmo q_MLast.cmo" -c swigp4.ml
bash-2.05a$ swig -ocaml -c++ -I$QTPATH/include qt.i bash-2.05a$ swig -ocaml -c++ -I$QTPATH/include qt.i
bash-2.05a$ mv qt_wrap.cxx qt_wrap.c bash-2.05a$ mv qt_wrap.cxx qt_wrap.c
bash-2.05a$ ocamlc -c -ccopt -xc++ -ccopt -g -g -ccopt -I$QTPATH/include qt_wrap.c bash-2.05a$ ocamlc -c -ccopt -xc++ -ccopt -g -g -ccopt -I$QTPATH/include qt_wrap.c
bash-2.05a$ ocamlc -c qt.mli bash-2.05a$ ocamlc -c qt.mli