Trends in Functional Programming

Abstract

Abstract. When testing a program, there are usually some parts that are rarely executed and hence more di cult to test. Finding inputs that guarantee that such parts are executed is an example of a reach problem, which in general seeks to ensure that targeted parts of a program are always executed. In previous work, Naylor and Runciman have developed a reachability solver for Haskell, based on the use of lazy narrowing from functional logic programming. Their work was focused on practical issues concerning implementation and performance. In this paper, we lay the groundwork for an underlying theory of such a system, by formally establishing the correctness of a simple reach solver.