One-Shot Algebraic Effects as Coroutines

This paper presents a translation from algebraic effects and handlers to asymmetric coroutines, which provides a simple, efficient and widely applicable implementation for the former. Algebraic effects and handlers are emerging as main-stream language technology to model effectful computations and attract attention not only from researchers but also from programmers. They are implemented in various ways as part of compilers, interpreters, or as libraries. We present a direct embedding of one-shot algebraic effects and handlers in a language which has asymmetric coroutines. The key observation is that, by restricting the use of continuations to be one-shot, we obtain a simple and sufficiently general implementation via coroutines, which are available in many modern programming languages. Our translation is a macro-expressible translation, and we have implemented its embedding as a library in Lua and Ruby, which allows one to write effectful programs in a modular way using algebraic effects and handlers.