This section discusses the functions used to communicate about
predicates. Though a Prolog predicate may be defined or not, redefined,
etc., a Prolog predicate has a handle that is neither destroyed nor
moved. This handle is known by the type predicate_t.
- predicate_t PL_pred(functor_t
f, module_t m)
- Return a handle to a predicate for the specified name/arity in the given
module. If the module argument m is
NULL, the
current context module is used. If the target predicate does not exist a
handle to a new undefined predicate is returned. The predicate
may fail, returning (predicate_t)0 after setting a resource
exception, if the target module has a limit on the
program_space, see set_module/1.
Currently aborts the process with a fatal error when out of
memory. Future versions may raise a resource exception and return (predicate_t)0.
- predicate_t PL_predicate(const
char *name, int arity, const char* module)
- Same as PL_pred(),
but provides a more convenient interface to the C programmer.
- void PL_predicate_info(predicate_t
p, atom_t *n, size_t *a, module_t *m)
- Return information on the predicate p. The name is stored
over
n, the arity over a, while m receives
the definition module. Note that the latter need not be the same as
specified with
PL_predicate().
If the predicate is imported into the module given to
PL_predicate(),
this function will return the module where the predicate is defined. Any
of the arguments n, a and m can be
NULL.