Exception Problem

[Vasco Pires]

Dear All,

I have a strange problem while calling Prolog from C.
In my project a call from C a Prolog predicate, that in some point 
calls a C function to validate some data.
The problem is that the prolog predicate returns an exception to the C 
code. The strange thing about this is that the C function that is 
called from prolog returns False, and consequently fails the predicate. 
If i comment this line and write Fail. The program works just fine and 
doesn't return the exception.


Here is my C code that calls prolog:

int plGetBasicDecision( char** name, int *argument, double *xPos, 
double *yPos, double *thetaPos )
{
  int func;
  WamWord arg[14];
  Bool res;
  int decision;

  func = Find_Atom("makeAdvancedDecision");
  Pl_Query_Begin(TRUE);

  arg[0] = Mk_Variable();
  arg[1] = Mk_Variable();
  arg[2] = Mk_Variable();
  arg[3] = Mk_Variable();
  arg[4] = Mk_Variable();
  arg[5] = Mk_Variable();

  res = Pl_Query_Call( func, 6, arg );

  if(res == 1) {
    decision = Rd_Integer(arg[0]);
    *name = Rd_String(arg[1]);
    *argument = Rd_Integer(arg[2]);
    *xPos = Rd_Float(arg[3]);
    *yPos = Rd_Float(arg[4]);
    *thetaPos = Rd_Float(arg[5]);
  } else {
    PlTerm except = Pl_Get_Exception();
    printf("Exception of type: %d\n\n", Type_Of_Term(except));
    decision = -1;
    name = NULL;
  }

  Pl_Query_End(TRUE);
  return decision;
}

Here is my prolog code that calls the C function:

fluentHasBall( Robot, s0 ) :-
        plRobotHasBall( Robot ).

it returns an exception, and if I change to this:

fluentHasBall( Robot, s0 ) :-
        fail.

it works just fine. the C function is:

Bool plRobotHasBall( char* Robot )
{

    return FALSE;
 }



Best Regards,
Vasco Pires


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