Dictionary lookup

Dictionary lookup in a binary tree

Source: The Art of Prolog

Program source code: dictionary_lookup.pl

/*	
    lookup(Key,Dictionary,Value) :-
	Dictionary contains the value indexed under Key.
	Dictionary is represented as an ordered binary tree.
 
*/
 
	lookup(Key,dict(Key,X,Left,Right),Value) :-
		!, X = Value.
	lookup(Key,dict(Key1,X,Left,Right),Value) :-
		Key < Key1 , lookup(Key,Left,Value).
	lookup(Key,dict(Key1,X,Left,Right),Value) :-
		Key > Key1, lookup(Key,Right,Value).
 
%	Program 15.9: Dictionary lookup in a binary tree