Newmain Ancestor example - help?

[raptor]

Interfacing C to gprolog:

I have downloaded gprolog and the newmain Ancestor example.  The code compiles and runs, but either generates an error or does not produce the expected results.  Loading the newmail.pl file in the gprolog interpreter does work, so I don't think the problem is the .pl file.

The problem seems to be with the Pl_Query_End(PL_RECOVER).  I tried changing it to use PL_KEEP_FOR_PROLOG, which runs, but does not give the correct set of solutions.

Has anybody else had this problem? Any recommendations or proposed fixes?

Below, I've provided information regarding the output, versions, source code etc.  Any help here is appreciated.

Jeff.


1. newmain Output (with PL_RECOVER) - generates error

        Enter a name (or 'end' to finish): peter

        Fatal Error: Pl_Query_End(PL_RECOVER) but unrecoverable query

2. newmain Output (with PL_KEEP_FOR_PROLOG): - runs, but incorrectly.

        Enter a name (or 'end' to finish): peter
            solution: mary
            solution: bob
            solution: jane
        3 solution(s)

Enter a name (or 'end' to finish):

3. the command used to compile:

        gplc -C '-Wall -g' newmain.pl newmain.c

4. versions, etc.
         Linux kernel version 2.4.18-14
         (cc version 3.2 20020903
         (Red Hat Linux 8.0 3.2-7))
         Prolog compiler (GNU Prolog) 1.2.16

5. the newmain.pl file contains:

parent(bob,mary).
parent(jane,mary).
parent(mary,peter).
parent(paul,peter).
parent(peter,john).

anc(X,Y):-
        parent(X,Y).

anc(X,Z):-
        parent(X,Y),
        anc(Y,Z).
   

6. the newmain.c source code.

static int
Main_Wrapper(int argc, char *argv[])
{
  int func;
  WamWord arg[10];
  char str[100];
  char *sol[100];
  int i, nb_sol = 0;
  Bool res;

  Start_Prolog(argc, argv);

  func = Find_Atom("anc");
  for (;;)
    {
      printf("\nEnter a name (or 'end' to finish): ");
      scanf("%s", str);

      if (strcmp(str, "end") == 0)
        break;

      Pl_Query_Begin(TRUE);

      arg[0] = Mk_Variable();
      arg[1] = Mk_String(str);
      nb_sol = 0;
      res = Pl_Query_Call(func, 2, arg);
      while (res)
        {
          sol[nb_sol++] = Rd_String(arg[0]);
          res = Pl_Query_Next_Solution();
        }
      Pl_Query_End(PL_RECOVER);

      for (i = 0; i < nb_sol; i++)
        printf("  solution: %s\n", sol[i]);
      printf("%d solution(s)\n", nb_sol);
    }

  Stop_Prolog();
  return 0;
}

int
main(int argc, char *argv[])
{
  return Main_Wrapper(argc, argv);
}