Parametric subtyping for structural parametric polymorphism

authors: Henry DeYoung, Andreia Mordido, Frank Pfenning, Ankush Das
year: 2023
url: http://arxiv.org/abs/2307.13661
publisher:
abstract: We study the interaction of structural subtyping with parametric polymorphism and recursively defined type constructors. Although structural subtyping is undecidable in this setting, we describe a notion of parametricity for type constructors and then exploit it to define parametric subtyping, a conceptually simple, decidable, and expressive fragment of structural subtyping that strictly generalizes rigid subtyping. We present and prove correct an effective saturation-based decision procedure for parametric subtyping, demonstrating its applicability using a variety of examples. We also provide an implementation of this decision procedure online.