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 as an artifact.

@article{paperbot2658,
  title = {Parametric Subtyping for Structural Parametric Polymorphism},
  author = {Henry DeYoung and Andreia Mordido and Frank Pfenning and Ankush Das},
  journal = {Proceedings of the ACM on Programming Languages},
  volume = {8},
  number = {POPL},
  year = {2024},
  doi = {10.1145/3632932}
}