Parallel Algebraic Effect Handlers

Algebraic effects and handlers support composable and structured control-flow abstraction. However, existing designs of algebraic effects often require effects to be executed sequentially. This paper studies parallel algebraic effect handlers. In particular, we formalize λp, an untyped lambda calculus which models two key features, effect handlers and parallelizable computations, the latter of which takes the form of a for expression as inspired by the Dex programming language. We present various interesting examples expressible in our calculus, and provide a Haskell implementation. We hope this paper provides a basis for future designs and implementations of parallel algebraic effect handlers.