external(+PredSpec, +CName)

+PredSpec

Of the form Atom/Integer (predicate name/arity).

+CName

Atom or string.

Description

If the visibility of PredSpec is not declared, it is set to local.

If necessary, an underscore is prepended to CName to get its form as used by the C compiler.

If a call to PredSpec has already been compiled as a Prolog call or a non-deterministic external call, error 62 is raised (``inconsistent procedure redefinition''). This can be prevented by defining the external before compiling any call to it or by using the declaration predicate external/1.

Fail Conditions

Resatisfiable

Exceptions

(4) instantiation fault

Either PredSpec or CName is not instantiated.

(5) type error

PredSpec is not of the form Atom/Integer.

(5) type error

CName is not an atom or a string.

(62) inconsistent procedure redefinition

A call to PredSpec has already been compiled as a Prolog call or a non-deterministic external call.

(211) External function does not exist

External function does not exist.

Examples

Assume we have the C++ file eg_cc_external.cc:

    #include "eclipseclass.h"
    extern "C" int
    p_sumlist()
    {
	int res;
	long x, sum = 0;
	EC_word list(EC_arg(1));
	EC_word car,cdr;

	for ( ; list.is_list(car,cdr) == EC_succeed; list = cdr)
	{
	    res = car.is_long(&x);
	    if (res != EC_succeed) return res;
	    sum += x;
	}
	res = list.is_nil();
	if (res != EC_succeed) return res;
	return unify(EC_arg(2), EC_word(sum));
    }


Compile that into a dynamic library, e.g. using g++ on a Linux machine:

    g++ -I/usr/local/eclipse/include/i386_linux -shared \
    	-o eg_cc_external.so eg_cc_external.cc


Load the .so file dynamically into Eclipse and declare the external:

      ?- load('eg_cc_external.so').
      yes.

      ?- external(sumlist/2, p_sumlist).
      yes.

      ?- sumlist([1,2,3,4,5],S).
      S = 15
      yes.


Errors:
      external(PredSpec, "p_member"). (Error 4).
      external(p/0, S).               (Error 4).
      external('p/0', p_p0).          (Error 5).
      external(p/0, 123).             (Error 5).
      external(prmsg/1, nosuchfunc).  (Error 211).

      ?- [user].
       p :- a.
       user   compiled 32 bytes in 0.00 seconds
      yes.
      ?- external(a/0, c_a).   (Error 62).

See Also