Subtyping, recursion, and parametric polymorphism in kernel fun

  • Authors:
  • Dario Colazzo;Giorgio Ghelli

  • Affiliations:
  • Dipartimento d'Informatica, Università di Pisa, Via F. Buonarroti 2, 56127 Pisa, Italy;Dipartimento d'Informatica, Università di Pisa, Via F. Buonarroti 2, 56127 Pisa, Italy

  • Venue:
  • Information and Computation
  • Year:
  • 2005

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Abstract

We study subtype checking for recursive types in system kernel Fun, a typed λ-calculus with subtyping and bounded second-order polymorphism. Along the lines of [ACM Transactions on Programming Languages and Systems, 15(4) (1993) 575], we define a subtype relation over kernel Fun recursive types, and prove it to be transitive. We then show that the natural extension of the algorithm introduced in [ACM Transactions on Programming Languages and Systems, 15(4) (1993) 575] to compare first-order recursive types yields a non-complete algorithm. Finally, we prove the completeness and correctness of a different algorithm, which lends itself to efficient implementations.