2026-07-26T21:31:43Z https://drops.dagstuhl.de/oai

oai:drops-oai.dagstuhl.de:18210 2024-03-06T11:01:23Z ddc:004 open_access

Restrictable Variants: A Simple and Practical Alternative to Extensible Variants Madsen, Magnus Starup, Jonathan Lindegaard Lutze, Matthew restrictable variants extensible variants refinement types Boolean unification We propose restrictable variants as a simple and practical alternative to extensible variants. Restrictable variants combine nominal and structural typing: a restrictable variant is an algebraic data type indexed by a type-level set formula that captures its set of active labels. We introduce new pattern-matching constructs that allows programmers to write functions that only match on a subset of variants, i.e., pattern-matches may be non-exhaustive. We then present a type system for restrictable variants which ensures that such non-exhaustive matches cannot get stuck at runtime. An essential feature of restrictable variants is that the type system can capture structure-preserving transformations: specifically the introduction and elimination of variants. This property is important for writing reusable functions, yet many row-based extensible variant systems lack it. In this paper, we present a calculus with restrictable variants, two partial pattern-matching constructs, and a type system that ensures progress and preservation. The type system extends Hindley-Milner with restrictable variants and supports type inference with an extension of Algorithm W with Boolean unification. We implement restrictable variants as an extension of the Flix programming language and conduct a few case studies to illustrate their practical usefulness. Schloss Dagstuhl – Leibniz-Zentrum für Informatik Magnus Madsen and Jonathan Lindegaard Starup and Matthew Lutze 2023 Is Part Of LIPIcs, Volume 263, 37th European Conference on Object-Oriented Programming (ECOOP 2023) InProceedings Text doc-type:ResearchArticle publishedVersion application/pdf doi:10.4230/LIPIcs.ECOOP.2023.17 urn:nbn:de:0030-drops-182109 https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2023.17 eng https://creativecommons.org/licenses/by/4.0/legalcode