Roger Bosman ; Birthe van den Berg ; Wenhao Tang ; Tom Schrijvers - A Calculus for Scoped Effects & Handlers

lmcs:11234 - Logical Methods in Computer Science, November 22, 2024, Volume 20, Issue 4 - https://doi.org/10.46298/lmcs-20(4:17)2024
A Calculus for Scoped Effects & HandlersArticle

Authors: Roger Bosman ; Birthe van den Berg ; Wenhao Tang ; Tom Schrijvers

    Algebraic effects & handlers have become a standard approach for side-effects in functional programming. Their modular composition with other effects and clean separation of syntax and semantics make them attractive to a wide audience. However, not all effects can be classified as algebraic; some need a more sophisticated handling. In particular, effects that have or create a delimited scope need special care, as their continuation consists of two parts-in and out of the scope-and their modular composition introduces additional complexity. These effects are called scoped and have gained attention by their growing applicability and adoption in popular libraries. While calculi have been designed with algebraic effects & handlers built in to facilitate their use, a calculus that supports scoped effects & handlers in a similar manner does not yet exist. This work fills this gap: we present $\lambda_{\mathit{sc}}$, a calculus with native support for both algebraic and scoped effects & handlers. It addresses the need for polymorphic handlers and explicit clauses for forwarding unknown scoped operations to other handlers. Our calculus is based on Eff, an existing calculus for algebraic effects, extended with Koka-style row polymorphism, and consists of a formal grammar, operational semantics, a (type-safe) type-and-effect system and type inference. We demonstrate $\lambda_{\mathit{sc}}$ on a range of examples.


    Volume: Volume 20, Issue 4
    Published on: November 22, 2024
    Accepted on: August 14, 2024
    Submitted on: April 24, 2023
    Keywords: Computer Science - Programming Languages