Implementing Equational Constraints in a Functional Language

by Bernd Braßel, Michael Hanus, Björn Peemöller, Fabian Reck

Proc. of the 19th International Conference on Applications of Declarative Programming and Knowledge Management (INAP 2011) and the 25th Workshop on Logic Programming (WLP 2011), INFSYS Research Report 1843-11-06 (TU Wien), pp. 22-33, 2011

KiCS2 is a new system to compile functional logic programs of the source language Curry into purely functional Haskell programs. The implementation is based on the idea to represent the search space as a data structure and logic variables as operations that generate their values. This has the advantage that one can apply various, and in particular, complete search strategies to compute solutions. However, the generation of all values for logic variables might be inefficient for applications that exploit constraints on partially known values. To overcome this drawback, we propose new techniques to implement equational constraints in this framework. In particular, we show how unification modulo function evaluation and functional patterns can be added without sacrificing the efficiency of the kernel implementation.

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