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16.5  Decomposing Attributed Variables

The attributes of an attributed variable can be accessed using one-way unification in a matching clause, e.g.
    get_attribute(X{Name:Attribute}, A) :-
        -?->
        A = Attribute.
This clause succeeds only when the first argument is an attributed variable, and it binds X to the whole attributed variable and A to the attribute with name Name. Note that a normal (unification) clause can not be used to decompose an attributed variable (it would create a new attributed variable and unify this with the caller argument, but the unification is handled by an attributed variable handler, see Section 16.7).


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