A Call-by-Need Strategy for Higher-Order Functional-Logic Programming

We present an approach to truely higher order functional logic programming based on higher order narrowing Roughly speaking we model a higher order functional core language by higher order rewriting and extend it by logic variables For the integration of logic programs conditional rules are supported For solving goals in this framework we present a complete calcu lus for higher order conditional narrowing We develop several re nements that utilize the determinism of functional programs These re nements can be combined to a narrowing strategy which generalizes call by need as in functional programming where the dedicated higher order methods are only used for full higher order goals Furthermore we propose an implementa tional model for this narrowing strategy which delays computations until needed