Implementing Disequality in a Lazy Functional Logic Language

H. Kuchen, F.J. Lopez Fraguas, J.J. Moreno Navarro, M. Rodriguez Artalejo

	   In this paper,we investigate an implementation of a lazy
	   functional logic language (in particular the language BABEL)
	   which uses disequality constraints for solving equations and
	   building answers.  We specify a new operational semantics
	   which combines lazy narrowing with disequality constraints
	   and we define an abstract machine tailored to the execution
	   of BABEL programs according to this semantics. The machine
	   is designed as a quite natural extension of a lazy graph
	   narrowing machine. Disjunctions of disequalities are handled
	   using the backtracking mechanism.