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Summary: Godel with User-de ned Evaluable Functions
Vision for the Future of Logic Programming: Laying the Foundations of a Modern Successor to Prolog. A
Workshop in Association with the International Logic Programming Symposium. Portland, OR, Dec. 1995,
pages 37{46.
Sergio Antoy David Shapiro Janet Vorvick
Portland State University
Abstract
We report our experience extending a logic programming language with a rst-order functional
component. Functional expressions are evaluated by narrowing and can contain logic variables
for a seamless integration with the logic component of the language. Our experiment shows
that our extension is achievable with a modest e ort. It also suggests some changes to the
syntax and semantics of the initial logic component of the language that would ease the use and
implementation of the functional component.
1 Introduction
Logic languages may bene t from allowing the de nition of functions in addition to predicates
and performing functional computations in addition to logic computations. A signi cant problem
presented by the presence of functions in a logic language is this: what shall we do when a function is
applied to arguments that are (or contain) logic variables. A solution to this problem is narrowing.
The focus of this note is on narrowing as the means for the integration of functional and logic
computations. Our speci c goals are the application of needed narrowing and the implementation
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