Towards a comprehensive theory of monadic effects

Abstract

It has been more than 20 years since monads were proposed as a unifying concept for computational effects, in both formal semantics and functional programs. Over that period, there has been substantial incremental progress on several fronts within the ensuing research area, including denotational, operational, and axiomatic characterizations of effects; principles and frameworks for combining effects; prescriptive vs. descriptive effect-type systems; specification vs. implementation of effects; and realizations of effect-related theoretical constructions in practical functional languages, both eager and lazy. Yet few would confidently claim that programs with computational effects are by now as well understood, and as thoroughly supported by formal reasoning techniques, as types and terms in purely functional settings.