Compilation of Effect Handlers and their Applications in Concurrency

Algebraic effects combined with effect handlers have emerged as compelling, modular abstraction for modelling and controlling computational effects. By separating the effect signatures from their implementation, algebraic effects afford a high degree of modularity as programmers can describe effectful computations independently of their concrete interpretation. We present a compiler for the functional programming language Links that uses the Multicore OCaml backend to provide a native implementation of effect handlers. We present a core calculus λρeff with row-polymorphic effects and effect handlers based on a variation of A-normal form used in our implementation. In addition, we give an operational semantics for the calculus. Furthermore, we describe a translation from λρeff to a subset of the intermediate language used by OCaml. Interestingly, concurrency can be described as an algebraic effect, whose handler amounts to a scheduler. Thus, rather than baking concurrency support into the compiler, we keep the compiler lean by implementing the message-passing concurrency model of Links using handlers. We demonstrate a faithful encoding of the concurrency model, which maintains type-safe communication by taking advantage of the effect system of Links. Finally, we perform some experiments with the compiler using the concurrency implementation to see how it performs against the Links interpreter. Moreover, we consider how to improve the performance of the compiler.