Calling Prolog from C

To make Prolog predicates callable from C, one has to replace the main.c file in the emulator with a new file that starts his/her own application. The following function must be executed before any call to Prolog predicates is executed:

       initialize_bprolog(int argc, char *argv[])

In addition, the environment variable BPDIR must be set correctly to be the home directory where B-Prolog is installed. The function initialize_bprolog() allocates all the stacks used in B-Prolog, initializes them, and loads the byte code file bp.out into the program area. There are two possible ways to call B-Prolog.

• int call_bprolog_string(char *goal) This function executes the Prolog call as represented by the string goal. The return value is 1 if the call succeeds and 0 if the call fails. The following shows several example calls:

  
          call_bprolog_string("load(myprog)")
          call_bprolog_string("X is 1+1")
          call_bprolog_string("p(X,Y),q(Y,Z)")
  

• call_bprolog_term(TERM goal) This function is similar to the previous one, but executes the Prolog call as represented by the term goal. While call_bprolog_string cannot return any result except for truth and failure from Prolog, this function can return results through Prolog variables in goal.

There is no means to let B-Prolog do backtracking from C. Therefore, if multiple solutions are required, the Prolog program has to return all the solutions through one call.