SWI-Prolog -- clause

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- Reference manual
  - Built-in Predicates
    - Examining the program
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Availability:built-in

clause_property(+ClauseRef, -Property)

Queries properties of a clause. ClauseRef is a reference to a clause as produced by clause/3, nth_clause/3 or prolog_frame_attribute/3. Unlike most other predicates that access clause references, clause_property/2 may be used to get information about erased clauses that have not yet been reclaimed. Property is one of the following:

file(FileName): Unify FileName with the name of the file from which the clause is loaded. Fails if the clause was not created by loading a file (e.g., clauses added using assertz/1). See also source.
line_count(LineNumber): Unify LineNumber with the line number of the clause. Fails if the clause is not associated to a file.
size(SizeInBytes): True when SizeInBytes is the size that the clause uses in memory in bytes. The size required by a predicate also includes the predicate data record, a linked list of clauses, clause selection instructions and optionally one or more clause indexes.
source(FileName): Unify FileName with the name of the source file that created the clause. This is the same as the file property, unless the file is loaded from a file that is textually included into source using include/1. In this scenario, file is the included file, while the source property refers to the main file.
fact: True if the clause has no body.
erased: True if the clause has been erased, but not yet reclaimed because it is referenced.
predicate(PredicateIndicator): PredicateIndicator denotes the predicate to which this clause belongs. This is needed to obtain information on erased clauses because the usual way to obtain this information using clause/3 fails for erased clauses.
module(Module): Module is the context module used to execute the body of the clause. For normal clauses, this is the same as the module in which the predicate is defined. However, if a clause is compiled with a module qualified head, the clause belongs to the predicate with the qualified head, while the body is executed in the context of the module in which the clause was defined.