Our paper “Type-Level Programming with Match Types” (Olivier Blanvillain, Jonathan Brachthäuser
Head of the SE research groupJonathan Immanuel Brachthäuser, Maxime Kjaer, and Martin Odersky) has been accepted for publication at the ACM SIGPLAN Symposium on Principles of Programming Languages (POPL 2022).

Abstract

Type-level programming is becoming more and more popular in the realm of functional programming. However, the combination of type-level programming and subtyping remains largely unexplored in practical programming languages. This paper presents match types, a type-level equivalent of pattern matching. Match types integrate seamlessly into programming languages with subtyping and, despite their simplicity, offer significant additional expressiveness. We formalize the feature of match types in a calculus based on System F sub and prove its soundness. We practically evaluate our system by implementing match types in the Scala 3 reference compiler, thus making type-level programming readily available to a broad audience of programmers.

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