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| <H1><a name="Chicken">23 SWIG and Chicken</a></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="#Chicken_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">23.1 Preliminaries</a></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="#Chicken_collection">Garbage collection</a> |
| section below. |
| </p> |
| |
| <p> |
| You may want to look at any of the examples in Examples/chicken/ |
| directory for the basic steps to run SWIG CHICKEN. |
| </p> |
| |
| <H3><a name="Chicken_nn3">23.1.1 Running SWIG in C mode</a></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">23.1.2 Running SWIG in C++ mode</a></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">23.2 Code Generation</a></H2> |
| |
| |
| <H3><a name="Chicken_nn6">23.2.1 Naming Conventions</a></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">23.2.2 Modules</a></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">23.2.3 Constants and Variables</a></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#Customization_features">Features and the %feature directive</a> |
| for info on how to apply the %feature. |
| </p> |
| |
| <H3><a name="Chicken_nn9">23.2.4 Functions</a></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">23.2.5 Exceptions</a></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#Customization_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 |
| the Chicken manual on Exceptions |
| 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">23.3 TinyCLOS</a></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">23.4 Linkage</a></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">23.4.1 Static binary or shared library linked at compile time</a></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">23.4.2 Building chicken extension libraries</a></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 the |
| Loading-extension-libraries 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">23.4.3 Linking multiple SWIG modules with TinyCLOS</a></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">23.5 Typemaps</a></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">23.6 Pointers</a></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="Chicken_collection">23.6.1 Garbage collection</a></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#Customization_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">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">23.7 Unsupported features and known problems</a></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">23.7.1 TinyCLOS problems with Chicken version <= 1.92</a></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> |