Path: utzoo!attcan!uunet!husc6!rutgers!ucsd!nosc!humu!uhccux!todd
From: todd@uhccux.uhcc.hawaii.edu (Todd Ogasawara)
Newsgroups: comp.lang.prolog
Subject: Arity/Prolog & Microsoft C problem
Keywords: MS-DOS Microsoft C adding a predicate
Message-ID: <2115@uhccux.uhcc.hawaii.edu>
Date: 25 Jul 88 09:02:19 GMT
Organization: University of Hawaii
Lines: 54


Has anyone had a problem in creating evaluable predicates using  C
functions for the Arity/Prolog interpreter (API version 5.x) using
Microsoft C version 5.0 and the Arity/Prolog Compiler (APC version 5.x
with a 3/35/88 modification date)?  Here is the problem.  I can pass a
value from API to a C function but CANNOT pass a value from a C
function to API.  The number appears to get "part of the way" to the
Arity/Prolog but does not unify properly.  I did not have this problem
using API & APC version 4.0 with Microsoft 5.0 earlier this year.

Below you can see two simple predicates to be added to the Arity/Prolog
interpreter.  The first, foo, declares the C function to be a predicate
with an arity of 2.  The C function simply takes an integer value in
and spits the value incremented by 1 out.  Unfortunately, although the
value is taken in correctly and something seems to be passed back to
API, the value does not unify properly with the predicate variable.
For example -- foo(1,X), write(X) -- fails.  The second predicate, zot,
is simply there to test if the Arity/Prolog Compiler and Microsoft
linker works at least for Prolog-only cases.  It does the same thing
foo does -- take in an integer value and increment it by one.  When
this is added as an evaluable predicate to API, it works.  E.g.,
zot(1,X), write(X). -- works as expected.

Has anyone else had the problem I described above?

%%% Arity/Prolog code to declare C function as a predicate
:- extrn foo/2:c('_foo').
:- visible foo/2.

%%% does the same thing as the C function
:- visible zot/2.

zot(In,Out) :-
        Out is In + 1.

/* ---- C function to be added as an evaluable predicate ---- */
#include	<apctype.h>

foo(ariin,ariout)
reftype	ariin;	/* integer coming in */
reftype	ariout;	/* integer going out */
{
	unsigned int	cint;

	if (getint_c(ariin,&cint) !=0 )
		return putint_c((int) ++cint, ariout);
	else
		return FAILURE;
}
-- 
Todd Ogasawara, U. of Hawaii Faculty Development Program
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