30 SWIG and Common Lisp

Common Lisp is a high-level, all-purpose, object-oriented, dynamic, functional programming language with long history. Common Lisp is used in many fields, ranging from web development to finance, and also common in computer science education. There are more than 9 different implementations of common lisp which are available, all have different foreign function interfaces. SWIG currently supports only the Allegro Common Lisp, CLisp and UFFI foreign function interfaces.

30.1 Allegro Common Lisp

30.2 CLISP

CLISP is a feature-loaded implementation of common lisp which is portable across most of the operating system environments and hardware. CLISP includes an interpreter, a compiler, a debugger, CLOS, MOP, a foreign language interface, i18n, regular expressions, a socket interface, and more. An X11 interface is available through CLX, Garnet and CLUE/CLIO. Command line editing is provided by readline. CLISP runs Maxima, ACL2 and many other Common Lisp packages.
To run the SWIG module of clisp requires very little effort, you just need to execute: 

swig -clispcl -module module-name   file-name
Because of the high level nature of the CLISP FFI, the bindings generated by SWIG may not be absolutely correct, and you may need to modify them. The good thing is that you don't need to complex interface file for the CLISP module. The CLISP module tries to produce code which is both human readable and easily modifyable.

30.2.1 Additional Commandline Options

The following table list the additional commandline options available for the CLISP module. They can also be seen by using: 

swig -clisp -help

CLISP specific options
-extern-all If this option is given then clisp definitions for all the functions
and global variables will be created otherwise only definitions for
externed functions and variables are created.
-generate-typedef If this option is given then def-c-type will be used to generate
shortcuts according to the typedefs in the input.

30.2.2 Details on CLISP bindings

As mentioned earlier the CLISP bindings generated by SWIG may need some modifications. The clisp module creates a lisp file with the same name as the module name. This lisp file contains a 'defpackage' declaration, with the package name same as the module name. This package uses the 'common-lisp' and 'ffi' packages. Also, package exports all the functions, structures and variables for which an ffi binding was generated.
After generating the defpackage statement, the clisp module also sets the default language. 

(defpackage :test
    (:use :common-lisp :ffi)
  (:export
   :make-bar
   :bar-x
   :bar-y
   :bar-a
   :bar-b
   :bar-z
   :bar-n
   :pointer_func
   :func123
   :make-cfunr
   :lispsort_double
   :test123))

(in-package :test)

(default-foreign-language :stdc)

The ffi wrappers for functions and variables are generated as shown below. When functions have arguments of type "double * array", SWIG doesn't knows whether it is an 'out' argument or it is an array which will be passed, so SWIG plays it safe by declaring it as an '(array (ffi:c-ptr DOUBLE-FLOAT))'. For arguments of type "int **z[100]" where SWIG has more information, i.e., it knows that 'z' is an array of pointers to pointers of integers, SWIG defines it to be '(z (ffi:c-ptr (ffi:c-array (ffi:c-ptr (ffi:c-ptr ffi:int)) 100)))' 

extern "C" {
int pointer_func(void (*ClosureFun)( void* _fun, void* _data, void* _evt ), int y);

int func123(div_t * x,int **z[100],int y[][1000][10]);

void lispsort_double (int n, double * array);

void test123(float x , double y);

}

(ffi:def-call-out pointer_func
    (:name "pointer_func")
  (:arguments (ClosureFun (ffi:c-function (:arguments (arg0 (ffi:c-pointer NIL))
						      (arg1 (ffi:c-pointer NIL))
						      (arg2 (ffi:c-pointer NIL)))
					  (:return-type NIL)))
	      (y ffi:int))
  (:return-type ffi:int)
  (:library +library-name+))

(ffi:def-call-out func123
    (:name "func123")
  (:arguments (x (ffi:c-pointer div_t))
	      (z (ffi:c-ptr (ffi:c-array (ffi:c-ptr (ffi:c-ptr ffi:int)) 100)))
	      (y (ffi:c-ptr (ffi:c-ptr (ffi:c-array ffi:int (1000 10))))))
  (:return-type ffi:int)
  (:library +library-name+))


(ffi:def-call-out lispsort_double
    (:name "lispsort_double")
  (:arguments (n ffi:int)
	      (array (ffi:c-ptr DOUBLE-FLOAT)))
  (:return-type NIL)
  (:library +library-name+))

(ffi:def-call-out test123
    (:name "test")
  (:arguments (x SINGLE-FLOAT)
	      (y DOUBLE-FLOAT))
  (:return-type NIL)
  (:library +library-name+))

The module also handles strutcures and #define constants as shown below. SWIG automatically adds the constructors and accessors created for the struct to the list of symbols exported by the package. 

struct bar {
    short x, y;
    char a, b;
    int *z[1000];
    struct bar * n;
};

#define max 1000

(ffi:def-c-struct bar
    (x :type ffi:short)
  (y :type ffi:short)
  (a :type character)
  (b :type character)
  (z :type (ffi:c-array (ffi:c-ptr ffi:int) 1000))
  (n :type (ffi:c-pointer bar)))

(defconstant max 1000)

30.3 UFFI