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.

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.

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 ;


  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.