% File: gv.pro

%Line: Implantation of a global variable ADT

%%Essential Functionality

declear(Variable,Value) :-
		  assert(binding(Variable,Value)).

diplay_bindings :-
		binding(Variable,Value),
		write(Variable),write(' -> '),write(Value),nl,fail.
		display_bindings.

value_of(Variable,Value) :-
		   binding(Variable,Value).

bind(Variable,NewValue) :-
	       retract(binding(Variable,_)),
	       assert(binding(Variable,NewValue)).

undeclear(Variable) :-
		    retract(binding(Variable,_)).

%% Arithmetic operator functionality

inc(Variable) :-
	      value_of(Variable,X),
	      XP1 is X+1,
	      bind(Variable,XP1).

dec(Variable) :-
	      value_of(Variable,X),
	      XP1 is X-1,
	      bind(Variable,XP1).

add(Variable,Number) :-
	      value_of(Variable,OldValue),
	      NewValue is OldValue + Number,
	      bind(Variable,NewValue).

sub(Variable,Number) :-
	      value_of(Variable,OldValue),
	      NewValue is OldValue - Number,
	      bind(Variable,NewValue).