11.3.105 instance/2

Synopsis

instance(+Ref, -Term)

Unifies Term with the most general instance of the dynamic clause or recorded term indicated by the database reference Ref.

Arguments

Ref

db_reference, must be nonvar

Term

term

Description

Ref must be instantiated to a database reference to an existing clause or recorded term. instance/2 is not sensitive to the source module and can be used to access any clause, regardless of its module.

Exceptions

instantiation_error

if Ref is not instantiated

type_error

if Ref is not a syntactically valid database reference

existence_error

if Ref is a syntactically valid database reference but does not refer to an existing clause or recorded term.

Examples

     | ?- assert(foo:bar,R).
     
     R = '$ref'(771292,1)
     
     | ?- instance('$ref'(771292,1),T).
     
     T = (bar:-true)
     
     | ?- clause(H,B,'$ref'(771292,1)).
     
     no
     | ?- clause(foo:H,B,'$ref'(771292,1)).
     
     H = bar,
     B = true

See Also

ref-mdb-acl.