Result Directed Computing in a Functional Logic Language

In a functional logic language, especially in a constraint functional logic language, often the topmost constructor is known which an expression should be evaluated to. E.g. in a guarded expression b ! e, b should only be evaluated to true. Evaluating b to false would only waste resources and risk to run into an innnite computation. Hence, some kind of result directed computation can be used to reduce the search space by cutting uninteresting computations. One possibility to achieve this result direction is to integrate it into the abstract machine which is the basis for the runtime system. Here, we show how to achieve result directed computation by means of a program transformation. A runtime system without special facilities for result directed computing can be used to run the transformed programs. Thus, runtime overhead for result directed computing is avoided.