Section "neck"

As an optimization the system can directly perform neck goals if they belong to a deterministic built-in that do not modify the continuation. Unlike specials, which are registered via make_special(), they need to be registered via make_check(). Further evaluable foreign func-tions can be registered via make_arithmetic().

This new neck API is provided in the form of exec_deref(), exec_build(), exec_unify() and exec_eval() that should be used to implement deterministic built-in and evaluable functions. They depend on a state in the form of the current variable display. Since release 1.3.6 of Do-gelog Player the API can be used in any desired, possibly incomplete, order.

The following neck API calls are provided:

make_check(P): host language: The function returns an anonymous predicate for the deterministic built-in P.
make_arithmetic(P): host language: The function returns an anonymous predicate for the deterministic built-in P.
exec_deref(A): host language: Return the dereferencing of the argument A.
is_pending(A): host language: Return whether the argument A is the undefined or a place.
exec_build(A): host language: Return the dereferencing of the argument A.
exec_unify(A, T): host language: Determine whether the argument A and the term T unify.
exec_eval(A): host language: Return the evaluation of the argument A.