Efficient compilation of algebraic effects and handlers

The popularity of algebraic effect handlers as a programming language feature for user-defined computational effects is steadily growing. Yet, even though efficient runtime representations have already been studied, most handler-based programs are still much slower than hand-written code. In this paper we show that the performance gap can be drastically narrowed (in some cases even closed) by means of type-and-effect directed optimising compilation. Our approach consists of two stages. Firstly, we combine elementary source-to-source transformations with judicious function specialisation in order to aggressively reduce handler applications. Secondly, we show how to elaborate the source language into a handler-less target language in a way that incurs no overhead for pure computations. This work comes with a practical implementation: an optimizing compiler from Eff, an ML style language with algebraic effect handlers, to OCaml. Experimental evaluation with this implementation demonstrates that in a number of benchmarks, our approach eliminates much of the overhead of handlers and yields competitive performance with hand-written OCaml code.nrpages: 32status: publishe