Curry-style types for nominal terms

  • Authors:
  • Maribel Fernández;Murdoch J. Gabbay

  • Affiliations:
  • King's College London, Dept. Computer Science, London, UK;Heriot-Watt University, Dept. Mathematics and Computer Science, Riccarton, Edinburgh, UK

  • Venue:
  • TYPES'06 Proceedings of the 2006 international conference on Types for proofs and programs
  • Year:
  • 2006

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Abstract

We define a rank 1 polymorphic type system for nominal terms, where typing environments type atoms, variables and function symbols. The interaction between type assumptions for atoms and substitution for variables is subtle: substitution does not avoid capture and so can move an atom into multiple different typing contexts. We give typing rules such that principal types exist and are decidable for a fixed typing environment. a-equivalent nominal terms have the same types; a non-trivial result because nominal terms include explicit constructs for renaming atoms. We investigate rule formats to guarantee subject reduction. Our system is in a convenient Curry-style, so the user has no need to explicitly type abstracted atoms.