- meta_predicate +Head, ...
- Define the predicates referenced by the comma-separated list Head
as meta-predicates. Each argument of each head is a
meta argument specifier. Defined specifiers are given below.
are interpreted; the mode declarations
- The argument is a term that is used to reference a predicate with N
more arguments than the given argument term. For example:
- The argument is module-sensitive, but does not directly refer to a
predicate. For example:
- The argument is not module-sensitive and unbound on entry.
- The argument is not module-sensitive and the mode is unspecified.
- The argument is not module-sensitive and the mode is unspecified. The
is equivalent to
. It is accepted for compatibility reasons. The predicate predicate_property/2 reports arguments declared using
- The argument is not module-sensitive and bound (i.e., nonvar) on entry.
- This extension is used to denote the possibly
^-annotated goal of setof/3, bagof/3, aggregate/3 and aggregate/4. It is processed similar to‘0', but leaving the
- The argument is a DCG body. See phrase/3.
Each argument that is module-sensitive (i.e., marked 0..9,
) is qualified with the context module of the caller if it is not already qualified. The implementation ensures that the argument is passed as <module>:<term>, where <module> is an atom denoting the name of a module and <term> itself is not a
term where the first argument is an atom. Below is a simple declaration and a number of queries.
:- meta_predicate meta(0, +). meta(Module:Term, _Arg) :- format('Module=~w, Term = ~q~n', [Module, Term]).
?- meta(test, x). Module=user, Term = test ?- meta(m1:test, x). Module=m1, Term = test ?- m2:meta(test, x). Module=m2, Term = test ?- m1:meta(m2:test, x). Module=m2, Term = test ?- meta(m1:m2:test, x). Module=m2, Term = test ?- meta(m1:42:test, x). Module=42, Term = test
The meta_predicate/1 declaration is the portable mechanism for defining meta-predicates and replaces the old SWI-Prolog specific mechanism provided by the deprecated predicates module_transparent/1, context_module/1 and strip_module/3. See also section 6.16.