11.3.157 predicate_property/2

Synopsis

predicate_property(?Callable, ?PredProperty)

Unifies PredProperty with a predicate property of an existing predicate, and Callable with the most general term that corresponds to that predicate.

Arguments

:Callable

callable

The skeletal specification of a loaded predicate.

PredProperty

term

The various properties associated with Callable. Each loaded predicate will have one or more of the properties:

• one of the atoms built_in (for built-in predicates) or compiled or interpreted (for user defined predicates) or fd_constraint for FD predicates see Defining Primitive Constraints.
• the atom dynamic for predicates that have been declared dynamic (see Dynamic Declarations),
• the atom multifile for predicates that have been declared multifile (see Multifile Declarations),
• the atom volatile for predicates that have been declared volatile (see Volatile Declarations),
• one or more terms (block Term) for predicates that have block declarations (see Block Declarations),
• the atom exported or terms imported_from(ModuleFrom) for predicates exported or imported from modules (see ref-mod),
• the term (meta_predicate Term) for predicates that have meta-predicate declarations (see ref-mod-met).

Description

If Callable is instantiated then predicate_property/2 successively unifies PredProperty with the various properties associated with Callable.

If PredProperty is bound to a valid predicate property, then predicate_property/2 successively unifies Callable with the skeletal specifications of all loaded predicates having PredProperty.

If Callable is not a loaded predicate or PredProperty is not a valid predicate property, the call fails.

If both arguments are unbound, then predicate_property/2 can be used to backtrack through all currently defined predicates and their corresponding properties.

Examples

• Predicates acquire properties when they are defined:

            | ?- [user].
            | :- dynamic p/1.
            | p(a).
            | end_of_file.
            % user compiled 0.117 sec 296 bytes
            
            yes
            | ?- predicate_property(p(_), Property).
            
            Property = dynamic ;
            
            Property = interpreted ;
  

• To backtrack through all the predicates P imported into module m from any module:

            | ?- predicate_property(m:P, imported_from(_)).
  

• To backtrack through all the predicates P imported into module m1 from module m2:

            | ?- predicate_property(m1:P, imported_from(m2)).
  

• To backtrack through all the predicates P exported by module m:

            | ?- predicate_property(m:P, exported).
  

• A variable can also be used in place of a module atom to find the names of modules having a predicate and property association:

            | ?- predicate_property(M:f, imported_from(m1)).
  

  will return all modules M that import f/0 from m1.

See Also

ref-lps-ove.