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Explicit effect subtyping

Part of: Effects and Handlers

Published online by Cambridge University Press:  08 June 2020

GEORGIOS KARACHALIAS ,
MATIJA PRETNAR Open the ORCID record for MATIJA PRETNAR [Opens in a new window] ,
AMR HANY SALEH ,
STIEN VANDERHALLEN  and
TOM SCHRIJVERS Open the ORCID record for TOM SCHRIJVERS [Opens in a new window]
GEORGIOS KARACHALIAS
Affiliation:
Department of Computer Science, KU Leuven, Belgium Tweag I/O (e-mail: georgios.karachalias@tweag.io)
MATIJA PRETNAR
Affiliation:
Faculty of Mathematics and Physics, University of Ljubljana, Slovenia (e-mail: matija.pretnar@fmf.uni-lj.si)
AMR HANY SALEH
Affiliation:
Department of Computer Science, KU Leuven, Belgium (e-mails: ah.saleh@kuleuven.be; stienvdhallen@gmail.com; tom.schrijvers@kuleuven.be)
STIEN VANDERHALLEN
Affiliation:
Department of Computer Science, KU Leuven, Belgium (e-mails: ah.saleh@kuleuven.be; stienvdhallen@gmail.com; tom.schrijvers@kuleuven.be)
TOM SCHRIJVERS
Affiliation:
Department of Computer Science, KU Leuven, Belgium (e-mails: ah.saleh@kuleuven.be; stienvdhallen@gmail.com; tom.schrijvers@kuleuven.be)
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Abstract

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As popularity of algebraic effects and handlers increases, so does a demand for their efficient execution. Eff, an ML-like language with native support for handlers, has a subtyping-based effect system on which an effect-aware optimising compiler could be built. Unfortunately, in our experience, implementing optimisations for Eff is overly error-prone because its core language is implicitly typed, making code transformations very fragile. To remedy this, we present an explicitly typed polymorphic core calculus for algebraic effect handlers with a subtyping-based type-and-effect system. It reifies appeals to subtyping in explicit casts with coercions that witness the subtyping proof, quickly exposing typing bugs in program transformations. Our typing-directed elaboration comes with a constraint-based inference algorithm that turns an implicitly typed Eff-like language into our calculus. Moreover, all coercions and effect information can be erased in a straightforward way, demonstrating that coercions have no computational content. Additionally, we present a monadic translation from our calculus into a pure language without algebraic effects or handlers, using the effect information to introduce monadic constructs only where necessary.

Type
Research Article
Information
Journal of Functional Programming , Volume 30 , 2020 , e15
Copyright
© The Author(s) 2020. Published by Cambridge University Press

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