% Implementation of global variable ADT % Essential functionality declare(Variable, Value) :- assert(binding(Variable, Value)). display_bindings :- binding(Variable, Value), write(Variable), write(' -> '), write(Value), nl, fail. display_bindings. value_of(Variable, Value) :- binding(Variable, Value). bind(Variable, Value) :- retract(binding(Variable,_)), assert(binding(Variable, Value)). undeclare(Variable) :- retract(binding(Variable,_)). % Arithmetic operators inc(Variable) :- value_of(Variable, X), INC is X + 1, bind(Variable, INC). dec(Variable) :- value_of(Variable, X), DEC is X - 1, bind(Variable, DEC). add(Variable, X) :- value_of(Variable, V), VPX is V + X, bind(Variable, VPX). sub(Variable, X) :- value_of(Variable, V), VMX is V - X, bind(Variable, VMX). % Quality of life rules exit :- halt. quit :- halt.