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 the home directory where B-Prolog was 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. BP_ERROR is returned if the system cannot be initialized.

A query can be a string or a Prolog term, and a query can return one solution and multiple solutions as well.

• int bp_call_string(char *goal): This function executes the Prolog call as represented by the string goal. The return value is BP_TRUE if the call succeeds, BP_FALSE if the call fails, and BP_ERROR if an exception occurs. Examples:

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

• bp_call_term(TERM goal): This function is similar to the previous one, but executes the Prolog call as represented by the term goal. While bp_call_string cannot return any bindings for variables, this function can return results through the Prolog variables in goal. Example:

        TERM call = bp_build_structure("p",2);
        bp_call_term(call);
  

• bp_mount_query_string(char *goal): Mount goal as the next Prolog goal to be executed.

• bp_mount_query_string(TERM goal): Mount goal as the next Prolog goal to be executed.

• bp_next_solution(): Retrieve the next solution of the current goal. If no goal is mounted before this function, then the exception illegal_predicate will be raised and BP_ERROR will be returned as the result. If no further solution is available, the function returns BP_FALSE. Otherwise, the next solution is found.