Extensions: A Technique for Structuring Functional-Logic Programs

Monads are a technique widely used in functional programming languages to address many different problems. This paper presents extensions, a functional-logic programming technique that constitutes an alternative to monads in several situations. Extensions permit the definition of easily reusable functions in the same way as monads, but are based on simpler concepts taken from logic programming, and hence they lead to more appealing and natural definitions of types and functions. Moreover, extensions are compatible with interesting features typical of logic programming, like multiple modes of use, while monads are not.