Down with variables

Abstract

The subject of this paper is point-free functional programming in Haskell. By this we mean writing programs using categorically-inspired combinators, algebraic data types defined as fixed points of functors, and impicit recursion through the use of type-parameterized recursion patterns. This style of programming is appropriate for program calculation (reasoning about programs equationally), but difficult to actually use in practice - most programmers use a mixture of the above elements with explicit recursion and manipulation of arguments. In this paper we present a mechanism that allows programmers to convert classic point-wise code into point-free style, and a Haskell library that enables the direct execution of the resulting code. Together, they make possible the use of point-free either as a direct programming style or as a domain into which programs can be transformed before being subject to further manipulation.