Combining Lazy Narrowing with Disequality Constraints

We investigate an extension of a lazy functional logic language, which uses term disequations both in programs and in computed answers. The semantic properties of the language are derived from the fact that it can be viewed as an instance of the CFLP(X)-scheme proposed in [Lo92] for constraint functional logic programming. In particular, the operational semantics for CFLP(X) — so called lazy constrained narrowing — is a computation mechanism parameterized by a constraint solver over the underlying domain. We define a constraint solver for our language, whose properties ensure completeness. As a further step towards implementation, we present an executable Prolog specification of the operational semantics, which has been implemented on top of a Prolog system. Experimental results have shown good performance.