Our LIPS are sealed: Interfacing functional and logic programming systems

Abstract

We report on a technique for interfacing an untyped logic language to a statically polymorphically typed functional language (FL). Our key insight is that polymorphic types can be interpreted as “need to know” specifications on function arguments. This leads to a criterion for liberally yet safely invoking the FL to reduce application terms as required during unification in the logic language. This method, called P-unification, enriches the capabilities of each language while retaining the integrity of their individual semantics and implementation technologies. The results presented suggest that a Horn clause logic programming (HCLP) systems can utilize unmodified implementations of FL's to (i) manipulate untyped or dynamically typed data, even though the FL is statically typed; (ii) act lazily, even though the FL is strict, and (iii) build structures containing HCLP terms alien to the FL, such as unbound variables.