Effect handlers in scope

Abstract

Algebraic effect handlers are a powerful means for describing effectful computations. They provide a lightweight and orthogonal technique to define and compose the syntax and semantics of different effects. The semantics is captured by handlers, which are functions that transform syntax trees.Unfortunately, the approach does not support syntax for scoping constructs, which arise in a number of scenarios. While handlers can be used to provide a limited form of scope, we demonstrate that this approach constrains the possible interactions of effects and rules out some desired semantics.This paper presents two different ways to capture scoped constructs in syntax, and shows how to achieve different semantics by reordering handlers. The first approach expresses scopes using the existing algebraic handlers framework, but has some limitations. The problem is fully solved in the second approach where we introduce higher-order syntax.

A predicate transformer semantics for effects (functional pearl)

“…We hope that the composition of predicate transformers can be used to assign semantics to programs using a variety of different effectsÐmuch as we defined a semantics of mixed programs and specifications from their constituent parts. Similar ideas have already been explored when embedding algebraic effects in Haskell by Wu et al [2014].…”

Combining predicate transformer semantics for effects: a case study in parsing regular languages

“…To illustrate how the semantics mesh well with other forms of semantics, we do not use ptParser as semantics for Parser in the remainder. We give denotational semantics, in the form of an effect handler for Parser [26,35]: Note that dmatch has exactly the type of the previously defined match, conveniently allowing us to reuse the match semantics. In this way, the handler hParser "hides" the implementation detail that the Parser effect was used.…”

Concurrent System Programming with Effect Handlers

“…There are several alternatives to implement the continuations in effect handlers including free monadic interpretations [16,17,36], CPS translations [13,20], and runtime strategies. Multicore OCaml chooses the latter and uses a custom stack layout, efficiently supported by the runtime system.…”

“…Implementations of effect handlers Since their inception, several implementations of algebraic effect handlers have appeared, many of which are implemented as libraries in existing programming languages [5,15,16,17,18,30,36]. There are several other implementations that like Multicore OCaml provide language level support for effect handlers:…”