Successively unifies Name with the name of predicates
currently defined and Head with the most general term built
from Name and the arity of the predicate. This predicate
succeeds for all predicates defined in the specified module, imported to
it, or in one of the modules from which the predicate will be imported
if it is called.
Succeeds if Head refers to a predicate that has property
Property. Can be used to test whether a predicate has a
certain property, obtain all properties known for Head, find
all predicates having property or even obtaining all
information available about the current program. Property is
one of:
interpreted
Is true if the predicate is defined in Prolog. We return true on this
because, although the code is actually compiled, it is completely
transparent, just like interpreted code.
built_in
Is true if the predicate is locked as a built-in predicate. This implies
it cannot be redefined in its definition module and it can normally not
be seen in the tracer.
foreign
Is true if the predicate is defined in the C language.
dynamic
Is true if the predicate is declared dynamic using the dynamic/1
declaration.
multifile
Is true if the predicate is declared multifile using the multifile/1
declaration.
undefined
Is true if a procedure definition block for the predicate exists, but
there are no clauses in it and it is not declared dynamic. This is true
if the predicate occurs in the body of a loaded predicate, an attempt to
call it has been made via one of the meta-call predicates or the
predicate had a definition in the past. See the library package
check for example usage.
transparent
Is true if the predicate is declared transparent using the
module_transparent/1
declaration.
exported
Is true if the predicate is in the public list of the context module.
imported_from(Module)
Is true if the predicate is imported into the context module from module Module.
indexed(Head)
Predicate is indexed (see index/1)
according to Head. Head is a term whose name and
arity are identical to the predicate. The arguments are unified with `1'
for indexed arguments, `0' otherwise.
file(FileName)
Unify FileName with the name of the sourcefile in which the
predicate is defined. See also source_file/2.
line_count(LineNumber)
Unify LineNumber with the line number of the first clause of
the predicate. Fails if the predicate is not associated with a file. See
also source_file/2.
number_of_clauses(ClauseCount)
Unify ClauseCount to the number of clauses associated with
the predicate. Fails for foreign predicates.
`Do What I Mean' (`dwim') support predicate. Term is a term,
which name and arity are used as a predicate specification. Dwim
is instantiated with the most general term built from Name
and the arity of a defined predicate that matches the predicate
specified by
Term in the `Do What I Mean' sense. See dwim_match/2
for `Do What I Mean' string matching. Internal system predicates are not
generated, unless style_check(+dollar) is active.
Backtracking provides all alternative matches.
Succeeds when Head can be unified with a clause head and Body
with the corresponding clause body. Gives alternative clauses on
backtracking. For facts Body is unified with the atom true.
Normally clause/2
is used to find clause definitions for a predicate, but it can also be
used to find clause heads for some body template.
Equivalent to clause/2,
but unifies Reference with a unique reference to the clause
(see also assert/2, erase/1).
If Reference is instantiated to a reference the clause's head
and body will be unified with Head and Body.
Provides access to the clauses of a predicate using their index number.
Counting starts at 1. If Reference is specified it unifies Pred
with the most general term with the same name/arity as the predicate and
Index with the index-number of the clause. Otherwise the name
and arity of Pred are used to determine the predicate. If Index
is provided Reference will be unified with the clause
reference. If Index is unbound, backtracking will yield both
the indices and the references of all clauses of the predicate. The
following example finds the 2nd clause of member/2:
?- nth_clause(member(_,_), 2, Ref), clause(Head, Body, Ref).
Ref = 160088
Head = system : member(G575, [G578|G579])
Body = member(G575, G579)
