Pascal Interface

If the Pascal file p.p is compiled as shown below, then loading the Prolog file as shown will produce the indicated results.

                                        
p.p
     
     
     type
     alfa = packed array[1..10] of char;
     
     (* p1(+integer, [-integer]) *)
     function p1(a: integer32): integer32;
     begin
       p1 := a + 9;
     end;
     
     (* p2(-integer) *)
     procedure p2(var a: integer32);
     begin
       a := 99;
     end;
     
     (* p11(+atom, [-atom]) *)
     function p11(a: integer32) : integer32;
     begin
       p11 := a;
     end;
     
     (* p21(+atom, -atom) *)
     procedure p21(a: integer32; var b: integer32);
     begin
       b := a;
     end;
     
     (* p3(+float, [-float]) *)
     function p3(a: real) : real;
     begin
       p3 := a + 9.0;
     end;
     
     (* p4(-float) *)
     procedure p4(var a: real);
     begin
       a := 9.9;
     end;
     
     (* p5(+string(10), -string(10)) *)
     procedure p5(var s: alfa; var t: alfa);
     begin
             t := s;
     end;
     
     (* p6(-string(10)) *)
     procedure p6(var s: alfa);
     begin
             s := 'output';
     end;
     

At the command level:

     % pc -c p.p
     

Produces the object file.

                                       
p.pl
     
     
     foreign_file(p, [p1, p2, p11, p21, p3, p4, p5, p6]).
     
     foreign(p1,  pascal, p1(+integer, [-integer])).
     foreign(p2,  pascal, p2(-integer)).
     foreign(p11, pascal, p11(+atom, [-atom])).
     foreign(p21, pascal, p21(+atom, -atom)).
     foreign(p3,  pascal, p3(+float, [-float])).
     foreign(p4,  pascal, p4(-float)).
     foreign(p6,  pascal, p5(+string(10),-string(10))).
     foreign(p5,  pascal, p6(-string(10))).
     
     :- load_foreign_files([p], ['-lpc']),
        abolish(foreign_file,2),
        abolish(foreign,3).
     

Loading the Prolog file (see foreign/3) into Prolog and invoking the following query gives the following results:

     | ?- p1(1,X1), p2(X2), p11(foo,X11), p21(foo,X21), p3(1.5,X3), p4(X4),
          p5('parameter',X5), p6(X6).
     
     X1 = 10,
     X2 = 99,
     X11 = X21 = foo,
     X3 = 10.5,
     X4 = 9.89999,
     X5 = parameter,
     X6 = output ;
     
     no
     

Notes:

1. Passing of unsized strings (i.e. use of the string argument specification in a foreign/3 fact) is not supported in this interface since pc does not have a convention for passing variable length arrays. Instead, padded strings (the string(N) argument specification) must be used. Notice that the corresponding parameter of +string(N) declaration is actually a call by reference parameter in Pascal procedures.
2. The linker option -lpc must be included in the call to load_foreign_files/2 so that the foreign code routine will have access to the standard Pascal library.