GADTs Meet Subtyping

  • Gabriel Scherer
  • Didier Rémy
Part of the Lecture Notes in Computer Science book series (LNCS, volume 7792)


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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Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  • Gabriel Scherer
    • 1
  • Didier Rémy
    • 1
  1. 1.INRIARocquencourtFrance

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