/tutorial/backtracking/tiny_prolog/prolog_var.e

 1class PROLOG_VAR
 2inherit PROLOG_TERM
 3feature
 4	type: INTEGER is
 5		do
 6			if value = Void then
 7				Result = type_var
 8			else
 9				Result = value.type
10			end
11		end
12	deref: PROLOG_TERM is 
13		do
14			if value = Void then
15				Result := Current
16			else
17				Result := value
18			end	
19		end
20	value: PROLOG_TERM
21end