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arXiv · 1301.2903

GADTs meet subtyping

Gabriel Scherer·Didier Rémy
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Abstract

While generalized algebraic datatypes (\GADTs) are now considered well-understood, adding them to a language with a notion of subtyping comes with a few surprises. What does it mean for a \GADT parameter to be covariant? The answer turns out to be quite subtle. It involves fine-grained properties of the subtyping relation that raise interesting design questions. We allow variance annotations in \GADT definitions, study their soundness, and present a sound and complete algorithm to check them. Our work may be applied to real-world ML-like languages with explicit subtyping such as OCaml, or to languages with general subtyping constraints.

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Gabriel Scherer, Didier Rémy. 2013-01-14. GADTs meet subtyping. https://arxiv.org/abs/1301.2903

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