module 'data.ref.backtrackable' { new(Initial, Ref) :- 'kernel':ref_backtrackable_new(Initial, X), module Ref [Ref, X] { get(V) :- 'kernel':ref_backtrackable_get(X, V). set(V) :- 'kernel':ref_backtrackable_set(X, V). pretty = '\'data.ref.backtrackable\':'(Ref:get) }. new = 'data.ref.backtrackable':new(_). }