Predicate information

8.8 Predicate information

8.8.1 current_predicate/1

Templates

: current_predicate(?predicate_indicator)

Description

current_predicate(Pred) succeeds if there exists a predicate indicator of a defined procedure that unifies with Pred. All user defined procedures are found, whether static or dynamic. Internal system procedures whose name begins with ’$’ are not found. A user-defined procedure is found even when it has no clauses. A user-defined procedure is not found if it has been abolished. To conform to the ISO reference, built-in predicates are not found except if the strict_iso Prolog flag is switched off (section 8.22.1). This predicate is re-executable on backtracking.

Errors


Pred is neither a variable nor a predicate indicator		type_error(predicate_indicator, Pred)

Pred is a term Name/Arity and Arity is neither a variable nor an integer		type_error(integer, Arity)

Pred is a term Name/Arity and Name is neither a variable nor an atom		type_error(atom, Name)

Pred is a term Name/Arity and Arity is an integer < 0		domain_error(not_less_than_zero, Arity)

Pred is a term Name/Arity and Arity is an integer > max_arity flag (section 8.22.1)		representation_error(max_arity)

Portability

ISO predicate.

8.8.2 predicate_property/2

Templates

: predicate_property(?callable, ?predicate_property)

Description

predicate_property(Head, Property) succeeds if Head refers to a predicate that has a property Property. All user defined procedures and built-in predicates are found. Internal system procedures whose name begins with ’$’ are not found. This predicate is re-executable on backtracking.

Since version 1.4.0, predicate_property/2 no longer accepts a predicate indicator. Control constructs are now returned. Properties built_in_fd and control_construct now imply the property built_in.

Predicate properties:

static: if the procedure is static.
dynamic: if the procedure is dynamic.
private: if the procedure is private.
public: if the procedure is public.
monofile: if the procedure is monofile.
multifile: if the procedure is multifile.
user: if the procedure is a user-defined procedure.
built_in: if the procedure is a built-in predicate or a control construct.
built_in_fd: if the procedure is an FD built-in predicate.
control_construct: if the procedure is a control construct (section 7.2).
native_code: if the procedure is compiled in native code.
prolog_file(File): source file from which the procedure has been read.
prolog_line(Line): line number of the source file.
meta_predicate(Head): if the procedure is a meta-predicate unify Head with the head-pattern. The head-pattern is a compound term with the same name and arity as the predicate where each argument of the term is a meta argument specifier as follows:
integer N
the argument is a term that is used to reference a predicate with N more arguments than the given argument term (e.g. call(0)).
:
the argument is module sensitive, but does not directly refer to a predicate (e.g. consult(:)).
-
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 bound (i.e., nonvar) on entry.

Errors


Head is neither a variable nor a callable term		type_error(callable, Head)

Property is neither a variable nor a predicate property term		domain_error(predicate_property, Property)

Property = prolog_file(File) and File is neither a variable nor an atom		type_error(atom, File)

Property = prolog_line(Line) and Line is neither a variable nor an integer		type_error(integer, Line)

Portability

GNU Prolog predicate.