Decomposing Attributed Variables

## 17.5 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 whose name is the instantiation of 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 17.7).