Argument Passing and Control

If Prolog encounters a foreign predicate at run time it will call a function specified in the predicate definition of the foreign predicate. The arguments (1, ..., arity) pass the Prolog arguments to the goal as Prolog terms. Foreign functions should be declared of type foreign_t. Deterministic foreign functions have two alternatives to return control back to Prolog:

void

PL_succeed
  Succeed deterministically. PL_succeed is defined as ``return TRUE''.

void

PL_fail
  Fail and start Prolog backtracking. PL_fail is defined as ``return FALSE''.

• Non-deterministic Foreign Predicates