How to Use Guarded Functional Programming
Guarded functional programming (GFP) has been proposed as an approach to integrate functional programming, represented by equations and rewriting, and logic programming, represented by Horn clauses and SLD resolution. The basic programming constructs are guarded equations, i.e. equations conditioned by guards which are Horn logic goals. When an equation is applied to rewrite an expression, its guard must be solved first. If a guard has more than one solutions, only one is considered (committed choice). In an extension of GFP, list comprehensions can be used to collect all solutions of a goal (GFP*). This paper presents a systematic approach how to use GFP* with respect to a classification of functions and relations regarding non-determinism properties. A sample problem is described whereof a taxonomy of functions and relations is derived. It is shown how the programming constructs of GFP* reflect this taxonomy and a systematic solution of the sample problem is outlined.
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