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diff --git a/Doc/Manual/Chicken.html b/Doc/Manual/Chicken.html new file mode 100644 index 0000000..98372a0 --- /dev/null +++ b/Doc/Manual/Chicken.html @@ -0,0 +1,598 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<!-- Hand-written HTML --> +<html> +<head> +<title>SWIG and Chicken</title> +<link rel="stylesheet" type="text/css" href="style.css"> +</head> + +<body bgcolor="#ffffff"> + +<H1><a name="Chicken"></a>19 SWIG and Chicken</H1> +<!-- INDEX --> +<div class="sectiontoc"> +<ul> +<li><a href="#Chicken_nn2">Preliminaries</a> +<ul> +<li><a href="#Chicken_nn3">Running SWIG in C mode</a> +<li><a href="#Chicken_nn4">Running SWIG in C++ mode</a> +</ul> +<li><a href="#Chicken_nn5">Code Generation</a> +<ul> +<li><a href="#Chicken_nn6">Naming Conventions</a> +<li><a href="#Chicken_nn7">Modules</a> +<li><a href="#Chicken_nn8">Constants and Variables</a> +<li><a href="#Chicken_nn9">Functions</a> +<li><a href="#Chicken_nn10">Exceptions</a> +</ul> +<li><a href="#Chicken_nn11">TinyCLOS</a> +<li><a href="#Chicken_nn12">Linkage</a> +<ul> +<li><a href="#Chicken_nn13">Static binary or shared library linked at compile time</a> +<li><a href="#Chicken_nn14">Building chicken extension libraries</a> +<li><a href="#Chicken_nn15">Linking multiple SWIG modules with TinyCLOS</a> +</ul> +<li><a href="#Chicken_nn16">Typemaps</a> +<li><a href="#Chicken_nn17">Pointers</a> +<ul> +<li><a href="#collection">Garbage collection</a> +</ul> +<li><a href="#Chicken_nn18">Unsupported features and known problems</a> +<ul> +<li><a href="#Chicken_nn19">TinyCLOS problems with Chicken version <= 1.92</a> +</ul> +</ul> +</div> +<!-- INDEX --> + + + + <p> + This chapter describes SWIG's support of CHICKEN. CHICKEN is a + Scheme-to-C compiler supporting most of the language features as + defined in the <i>Revised^5 Report on Scheme</i>. Its main + attributes are that it + </p> + + <ol> + <li>generates portable C code</li> + <li>includes a customizable interpreter</li> + <li>links to C libraries with a simple Foreign Function Interface</li> + <li>supports full tail-recursion and first-class continuations</li> + </ol> + + <p> + When confronted with a large C library, CHICKEN users can use + SWIG to generate CHICKEN wrappers for the C library. However, + the real advantages of using SWIG with CHICKEN are its + <strong>support for C++</strong> -- object-oriented code is + difficult to wrap by hand in CHICKEN -- and its <strong>typed + pointer representation</strong>, essential for C and C++ + libraries involving structures or classes. + + </p> + +<H2><a name="Chicken_nn2"></a>19.1 Preliminaries</H2> + + + <p> + CHICKEN support was introduced to SWIG in version 1.3.18. SWIG + relies on some recent additions to CHICKEN, which are only + present in releases of CHICKEN with version number + <strong>greater than or equal to 1.89</strong>. + To use a chicken version between 1.40 and 1.89, see the <a href="#collection">Garbage collection</a> + section below. + </p> + + <p> + You may want to look at any of the examples in Examples/chicken/ + or Examples/GIFPlot/Chicken for the basic steps to run SWIG + CHICKEN. + </p> + +<H3><a name="Chicken_nn3"></a>19.1.1 Running SWIG in C mode</H3> + + + <p> + To run SWIG CHICKEN in C mode, use + the -chicken option. + </p> + + <div class="shell"> + <pre>% swig -chicken example.i</pre> + </div> + + <p> + To allow the wrapper to take advantage of future CHICKEN code + generation improvements, part of the wrapper is direct CHICKEN + function calls (<tt>example_wrap.c</tt>) and part is CHICKEN + Scheme (<tt>example.scm</tt>). The basic Scheme code must + be compiled to C using your system's CHICKEN compiler or + both files can be compiled directly using the much simpler <tt>csc</tt>. + </p> + + <div class="shell"> +<pre> +% chicken example.scm -output-file oexample.c +</pre> + </div> + + <p> + So for the C mode of SWIG CHICKEN, <tt>example_wrap.c</tt> and + <tt>oexample.c</tt> are the files that must be compiled to + object files and linked into your project. + </p> + +<H3><a name="Chicken_nn4"></a>19.1.2 Running SWIG in C++ mode</H3> + + + <p> + To run SWIG CHICKEN in C++ mode, use + the -chicken -c++ option. + </p> + + <div class="shell"> + <pre>% swig -chicken -c++ example.i</pre> + </div> + + <p> + This will generate <tt>example_wrap.cxx</tt> and + <tt>example.scm</tt>. The basic Scheme code must be + compiled to C using your system's CHICKEN compiler or + both files can be compiled directly using the much simpler <tt>csc</tt>. + </p> + + <div class="shell"> + <pre>% chicken example.scm -output-file oexample.c</pre> + </div> + + <p> + So for the C++ mode of SWIG CHICKEN, <tt>example_wrap.cxx</tt> + and <tt>oexample.c</tt> are the files that must be compiled to + object files and linked into your project. + </p> + +<H2><a name="Chicken_nn5"></a>19.2 Code Generation</H2> + + +<H3><a name="Chicken_nn6"></a>19.2.1 Naming Conventions</H3> + + + <p> + Given a C variable, function or constant declaration named + <tt>Foo_Bar</tt>, the declaration will be available + in CHICKEN as an identifier ending with + <tt>Foo-Bar</tt>. That is, an underscore is converted + to a dash. + </p> + + <p> + You may control what the CHICKEN identifier will be by using the + <tt>%rename</tt> SWIG directive in the SWIG interface file. + </p> + +<H3><a name="Chicken_nn7"></a>19.2.2 Modules</H3> + + + <p> + The name of the module must be declared one of two ways: + <ul> + <li>Placing <tt>%module example</tt> in the SWIG interface + file.</li> + <li>Using <tt>-module example</tt> on the SWIG command + line.</li> + </ul> + + <p> + The generated example.scm file then exports <code>(declare (unit modulename))</code>. + If you do not want SWIG to export the <code>(declare (unit modulename))</code>, pass + the -nounit option to SWIG. + + <p> + CHICKEN will be able to access the module using the <code>(declare + (uses <i>modulename</i>))</code> CHICKEN Scheme form. + </p> + +<H3><a name="Chicken_nn8"></a>19.2.3 Constants and Variables</H3> + + + <p> + Constants may be created using any of the four constructs in + the interface file: + </p> + <ol> + <li><code>#define MYCONSTANT1 ...</code></li> + <li><code>%constant int MYCONSTANT2 = ...</code></li> + <li><code>const int MYCONSTANT3 = ...</code></li> + <li><code>enum { MYCONSTANT4 = ... };</code></li> + </ol> + + <p> + In all cases, the constants may be accessed from within CHICKEN + using the form <tt>(MYCONSTANT1)</tt>; that is, the constants + may be accessed using the read-only parameter form. + </p> + + <p> + Variables are accessed using the full parameter form. + For example, to set the C variable "int my_variable;", use the + Scheme form <tt>(my-variable 2345)</tt>. To get the C variable, + use <tt>(my-variable)</tt>. + </p> + + <p> + The <tt>%feature("constasvar")</tt> can be applied to any constant + or immutable variable. Instead of exporting the constant as + a function that must be called, the constant will appear as a + scheme variable. This causes the generated .scm file to just contain the code + <tt>(set! MYCONSTANT1 (MYCONSTANT1))</tt>. See + <a href="Customization.html#features">Features and the %feature directive</a> + for info on how to apply the %feature. + </p> + +<H3><a name="Chicken_nn9"></a>19.2.4 Functions</H3> + + + <p> + C functions declared in the SWIG interface file will have + corresponding CHICKEN Scheme procedures. For example, the C + function "int sqrt(double x);" will be available using the + Scheme form <tt>(sqrt 2345.0)</tt>. A <code>void</code> return + value will give C_SCHEME_UNDEFINED as a result. + </p> + <p> + A function may return more than one value by using the + <code>OUTPUT</code> specifier (see Lib/chicken/typemaps.i). + They will be returned as multiple values using <code>(values)</code> if there is more than one + result (that is, a non-void return value and at least one argout + parameter, or a void return value and at least two argout + parameters). The return values can then be accessed with <code>(call-with-values)</code>. + </p> + +<H3><a name="Chicken_nn10"></a>19.2.5 Exceptions</H3> + + + <p>The SWIG chicken module has support for exceptions thrown from + C or C++ code to be caught in scheme. + See <a href="Customization.html#exception">Exception handling with %exception</a> + for more information about declaring exceptions in the interface file. + </p> + + <p>Chicken supports both the <code>SWIG_exception(int code, const char *msg)</code> interface + as well as a <code>SWIG_ThrowException(C_word val)</code> function for throwing exceptions from + inside the %exception blocks. <code>SWIG_exception</code> will throw a list consisting of the code + (as an integer) and the message. Both of these will throw an exception using <code>(abort)</code>, + which can be handled by <code>(handle-exceptions)</code>. See + <a href="http://www.call-with-current-continuation.org/manual/Exceptions.html#Exceptions">Chicken manual on Exceptions</a> + and <a href="http://srfi.schemers.org/srfi-12/srfi-12.html">SFRI-12</a>. Since the exception values are thrown + directly, if <code>(condition-case)</code> is used to catch an exception the exception will come through in the <code>val ()</code> case. + </p> + + <p>The following simple module</p> + +<div class="code"><pre> +%module exception_test + +%inline %{ + void test_throw(int i) throws (int) { + if (i == 1) throw 15; + } +%} +</pre></div> + + <p>could be run with</p> + +<div class="targetlang"><pre> +(handle-exceptions exvar + (if (= exvar 15) + (print "Correct!") + (print "Threw something else " exvar)) + (test-throw 1)) +</pre></div> + + +<H2><a name="Chicken_nn11"></a>19.3 TinyCLOS</H2> + + + <p> + The author of TinyCLOS, Gregor Kiczales, describes TinyCLOS as: + "Tiny CLOS is a Scheme implementation of a `kernelized' CLOS, with a + metaobject protocol. The implementation is even simpler than + the simple CLOS found in `The Art of the Metaobject Protocol,' + weighing in at around 850 lines of code, including (some) + comments and documentation." + </p> + + <p> + Almost all good Scheme books describe how to use metaobjects and + generic procedures to implement an object-oriented Scheme + system. Please consult a Scheme book if you are unfamiliar + with the concept. + </p> + + <p> + + CHICKEN has a modified version of TinyCLOS, which SWIG CHICKEN + uses if the -proxy argument is given. If -proxy is passed, then + the generated example.scm file will contain TinyCLOS class definitions. + A class named Foo is declared as <Foo>, and each member variable + is allocated a slot. Member functions are exported as generic functions. + + <p> + + Primitive symbols and functions (the interface that would be presented if + -proxy was not passed) are hidden and no longer accessible. If the -unhideprimitive + command line argument is passed to SWIG, then the primitive symbols will be + available, but each will be prefixed by the string "primitive:" + + <p> + + The exported symbol names can be controlled with the -closprefix and -useclassprefix arguments. + If -useclassprefix is passed to SWIG, every member function will be generated with the class name + as a prefix. If the -closprefix mymod: argument is passed to SWIG, then the exported functions will + be prefixed by the string "mymod:". If -useclassprefix is passed, -closprefix is ignored. + + </p> + +<H2><a name="Chicken_nn12"></a>19.4 Linkage</H2> + + + <p> + Please refer to <em>CHICKEN - A practical and portable Scheme + system - User's manual</em> for detailed help on how to link + object files to create a CHICKEN Scheme program. Briefly, to + link object files, be sure to add <tt>`chicken-config + -extra-libs -libs`</tt> or <tt>`chicken-config -shared + -extra-libs -libs`</tt>to your linker options. Use the + <tt>-shared</tt> option if you want to create a dynamically + loadable module. You might also want to use the much simpler + <tt>csc</tt> or <tt>csc.bat</tt>. + </p> + + <p>Each scheme file that is generated + by SWIG contains <code>(declare (uses <i>modname</i>))</code>. This means that to load the + module from scheme code, the code must include <code>(declare (uses <i>modname</i>))</code>. + </p> + + +<H3><a name="Chicken_nn13"></a>19.4.1 Static binary or shared library linked at compile time</H3> + + + <p>We can easily use csc to build a static binary.</p> + +<div class="shell"> +<pre> +$ swig -chicken example.i +$ csc -v example.scm example_impl.c example_wrap.c test_script.scm -o example +$ ./example +</pre> +</div> + +<p>Similar to the above, any number of <tt>module.scm</tt> files could be compiled +into a shared library, and then that shared library linked when compiling the +main application.</p> + +<div class="shell"> +<pre> +$ swig -chicken example.i +$ csc -sv example.scm example_wrap.c example_impl.c -o example.so +</pre> +</div> + +<p>The <tt>example.so</tt> file can then linked with <tt>test_script.scm</tt> when it +is compiled, in which case <tt>test_script.scm</tt> must have <code>(declare (uses example))</code>. +Multiple SWIG modules could have been linked into <tt>example.so</tt> and each +one accessed with a <code>(declare (uses ... ))</code>. +</p> + +<div class="shell"> +<pre> +$ csc -v test_script.scm -lexample +</pre> +</div> + +<p>An alternative is that the test_script.scm can have the code <code>(load-library 'example "example.so")</code>, +in which case the test script does not need to be linked with example.so. The test_script.scm file can then +be run with <tt>csi</tt>. +</p> + +<H3><a name="Chicken_nn14"></a>19.4.2 Building chicken extension libraries</H3> + + +<p>Building a shared library like in the above section only works if the library +is linked at compile time with a script containing <code>(declare (uses ...))</code> or is +loaded explicitly with <code>(load-library 'example "example.so")</code>. It is +not the format that CHICKEN expects for extension libraries and eggs. The problem is the +<code>(declare (unit <i>modname</i>))</code> inside the <tt>modname.scm</tt> file. There are +two possible solutions to this.</p> + +<p>First, SWIG accepts a <tt>-nounit</tt> argument, in which case the <code>(declare (unit <i>modname</i>))</code> +is not generated. Then, the <tt>modname.scm</tt> and <tt>modname_wrap.c</tt> files <b>must</b> be compiled into +their own shared library.</p> + +<div class="shell"> +<pre> +$ csc -sv modname.scm modname_wrap.c modname_impl.c -o modname.so +</pre> +</div> + +<p>This library can then be loaded by scheme code with the <code>(require 'modname)</code> function. +See <a href="http://www.call-with-current-continuation.org/manual/Loading-extension-libraries.html"> +Loading-extension-libraries</a> in the eval unit inside the CHICKEN manual for more information.</p> + +<p>Another alternative is to run SWIG normally and create a scheme file that contains <code>(declare (uses <i>modname</i>))</code> +and then compile that file into the shared library as well. For example, inside the <tt>mod_load.scm</tt> file,</p> + +<div class="targetlang"> +<pre> +(declare (uses mod1)) +(declare (uses mod2)) +</pre> +</div> + +<p>Which would then be compiled with</p> + +<div class="shell"> +<pre> +$ swig -chicken mod1.i +$ swig -chicken mod2.i +$ csc -sv mod_load.scm mod1.scm mod2.scm mod1_wrap.c mod2_wrap.c mod1_impl.c mod2_impl.c -o mod.so +</pre> +</div> + +<p>Then the extension library can be loaded with <code>(require 'mod)</code>. As we can see here, +<tt>mod_load.scm</tt> contains the code that gets executed when the module is loaded. All this code +does is load both mod1 and mod2. As we can see, this technique is more useful when you want to +combine a few SWIG modules into one chicken extension library, especially if modules are related by +<code>%import</code></p> + +<p>In either method, the files that are compiled into the shared library could also be +packaged into an egg. The <tt>mod1_wrap.c</tt> and <tt>mod2_wrap.c</tt> files that are created by SWIG +are stand alone and do not need SWIG to be installed to be compiled. Thus the egg could be +distributed and used by anyone, even if SWIG is not installed.</p> + +<p>See the <tt>Examples/chicken/egg</tt> directory in the SWIG source for an example that builds +two eggs, one using the first method and one using the second method.</p> + +<H3><a name="Chicken_nn15"></a>19.4.3 Linking multiple SWIG modules with TinyCLOS</H3> + + +<p>Linking together multiple modules that share type information using the <code>%import</code> +directive while also using <tt>-proxy</tt> is more complicated. For example, if <tt>mod2.i</tt> imports <tt>mod1.i</tt>, then the +<tt>mod2.scm</tt> file contains references to symbols declared in <tt>mod1.scm</tt>, +and thus a <code>(declare (uses <i>mod1</i>))</code> or <code>(require '<i>mod1</i>)</code> must be exported +to the top of <tt>mod2.scm</tt>. By default, when SWIG encounters an <code>%import "modname.i"</code> directive, +it exports <code>(declare (uses <i>modname</i>))</code> into the scm file. This works fine unless mod1 was compiled with +the <tt>-nounit</tt> argument or was compiled into an extension library with other modules under a different name.</p> + +<p>One option is to override the automatic generation of <code>(declare (uses mod1))</code> +by passing the <tt>-noclosuses</tt> option to SWIG when compiling <tt>mod2.i</tt>. +SWIG then provides the <code>%insert(closprefix) %{ %}</code> directive. Any scheme code inside that directive is inserted into the +generated .scm file, and if <tt>mod1</tt> was compiled with <tt>-nounit</tt>, the directive should contain <code>(require 'mod1)</code>. +This option allows for mixed loading as well, where some modules are imported with <code>(declare (uses <i>modname</i>))</code> +(which means they were compiled without -nounit) and some are imported with <code>(require 'modname)</code>.</p> + +<p>The other option is to use the second idea in the above section. Compile all the modules normally, without any +<code>%insert(closprefix)</code>, <tt>-nounit</tt>, or <tt>-noclosuses</tt>. Then the modules will import each other correctly +with <code>(declare (uses ...))</code>. +To create an extension library or an egg, just create a <tt>module_load.scm</tt> file that <code>(declare (uses ...))</code> +all the modules.</p> + +<H2><a name="Chicken_nn16"></a>19.5 Typemaps</H2> + + + <p> + The Chicken module handles all types via typemaps. This information is + read from <code>Lib/chicken/typemaps.i</code> and + <code>Lib/chicken/chicken.swg</code>. + </p> + +<H2><a name="Chicken_nn17"></a>19.6 Pointers</H2> + + + <p> + For pointer types, SWIG uses CHICKEN tagged pointers. + + A tagged pointer is an ordinary CHICKEN pointer with an + extra slot for a void *. With SWIG + CHICKEN, this void * is a pointer to a type-info + structure. So each pointer used as input or output from + the SWIG-generated CHICKEN wrappers will have type + information attached to it. This will let the wrappers + correctly determine which method should be called + according to the object type hierarchy exposed in the SWIG + interface files. + </p> + <p> + To construct a Scheme object from a C pointer, the wrapper code + calls the function + <code>SWIG_NewPointerObj(void *ptr, swig_type_info *type, int owner)</code>, + The function that calls <code>SWIG_NewPointerObj</code> must have a variable declared + <code>C_word *known_space = C_alloc(C_SIZEOF_SWIG_POINTER);</code> + It is ok to call <code>SWIG_NewPointerObj</code> more than once, + just make sure known_space has enough space for all the created pointers. + </p> + <p> + To get the pointer represented by a CHICKEN tagged pointer, the + wrapper code calls the function + <code>SWIG_ConvertPtr(C_word s, void **result, swig_type_info *type, int flags)</code>, + passing a pointer to a struct representing the expected pointer + type. flags is either zero or SWIG_POINTER_DISOWN (see below). + </p> + +<H3><a name="collection"></a>19.6.1 Garbage collection</H3> + + + <p>If the owner flag passed to <code>SWIG_NewPointerObj</code> is 1, <code>NewPointerObj</code> will add a + finalizer to the type which will call the destructor or delete method of + that type. The destructor and delete functions are no longer exported for + use in scheme code, instead SWIG and chicken manage pointers. + In situations where SWIG knows that a function is returning a type that should + be garbage collected, SWIG will automatically set the owner flag to 1. For other functions, + the <code>%newobject</code> directive must be specified for functions whose return values + should be garbage collected. See + <a href="Customization.html#ownership">Object ownership and %newobject</a> for more information. + </p> + + <p>In situations where a C or C++ function will assume ownership of a pointer, and thus + chicken should no longer garbage collect it, SWIG provides the <code>DISOWN</code> input typemap. + After applying this typemap (see the <a href="Typemaps.html">Typemaps chapter</a> for more information on how to apply typemaps), + any pointer that gets passed in will no longer be garbage collected. + An object is disowned by passing the <code>SWIG_POINTER_DISOWN</code> flag to <code>SWIG_ConvertPtr</code>. + <b>Warning:</b> Since the lifetime of the object is now controlled by the underlying code, the object might + get deleted while the scheme code still holds a pointer to it. Further use of this pointer + can lead to a crash. + </p> + + <p>Adding a finalizer function from C code was added to chicken in the 1.89 release, so garbage collection + does not work for chicken versions below 1.89. If you would like the SWIG generated code to work with + chicken 1.40 to 1.89, pass the <code>-nocollection</code> argument to SWIG. This will not export code + inside the _wrap.c file to register finalizers, and will then export destructor functions which + must be called manually. + </p> + +<H2><a name="Chicken_nn18"></a>19.7 Unsupported features and known problems</H2> + + + <ul> + <li>No director support.</li> + <li>No support for c++ standard types like std::vector.</li> + <li>The TinyCLOS wrappers for overloaded functions will not work correctly when using + <a href="SWIGPlus.html#SWIGPlus_default_args">%feature(compactdefaultargs)</a>.</li> + </ul> + +<H3><a name="Chicken_nn19"></a>19.7.1 TinyCLOS problems with Chicken version <= 1.92</H3> + + + <p>In Chicken versions equal to or below 1.92, TinyCLOS has a limitation such that generic methods do not properly work on methods + with different number of specializers: TinyCLOS assumes that every method added to a generic function + will have the same number of specializers. SWIG generates functions with different lengths of specializers + when C/C++ functions are overloaded. For example, the code</p> + +<div class="code"> +<pre> +class Foo {}; +int foo(int a, Foo *b); +int foo(int a); +</pre></div> + +<p>will produce scheme code</p> + +<div class="targetlang"> +<pre> +(define-method (foo (arg0 <top>) (arg1 <Foo>)) (<i>call primitive function</i>)) +(define-method (foo (arg0 <top>)) (<i>call primitive function</i>)) +</pre></div> + +<p>Using unpatched TinyCLOS, the second <code>(define-method)</code> will replace the first one, +so calling <code>(foo 3 f)</code> will produce an error.</p> + +<p>There are three solutions to this. The easist is to upgrade to the latest Chicken version. Otherwise, the +file <tt>Lib/chicken/tinyclos-multi-generic.patch</tt> in the SWIG source contains a patch against +tinyclos.scm inside the 1.92 chicken source to add support into TinyCLOS for multi-argument generics. (This patch was accepted into Chicken) +This requires chicken to be rebuilt and custom install of chicken. An alternative is the <tt>Lib/chicken/multi-generic.scm</tt> +file in the SWIG source. This file can be loaded after TinyCLOS is loaded, and it will override some functions +inside TinyCLOS to correctly support multi-argument generics. Please see the comments at the top of both files for more information.</p> + + </body> +</html> |