Associated types with class

  • Authors:

  • Manuel M. T. Chakravarty;Gabriele Keller;Simon Peyton Jones;Simon Marlow

  • Affiliations:

  • University of New South Wales, Australia;University of New South Wales, Australia;Microsoft Research Ltd., Cambridge, UK;Microsoft Research Ltd., Cambridge, UK

  • Venue:
  • Proceedings of the 32nd ACM SIGPLAN-SIGACT symposium on Principles of programming languages
  • Year:
  • 2005

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Abstract

Haskell's type classes allow ad-hoc overloading, or type-indexing, of functions. A natural generalisation is to allow type-indexing of data types as well. It turns out that this idea directly supports a powerful form of abstraction called associated types, which are available in C++ using traits classes. Associated types are useful in many applications, especially for self-optimising libraries that adapt their data representations and algorithms in a type-directed manner.In this paper, we introduce and motivate associated types as a rather natural generalisation of Haskell's existing type classes. Formally, we present a type system that includes a type-directed translation into an explicitly typed target language akin to System F; the existence of this translation ensures that the addition of associated data types to an existing Haskell compiler only requires changes to the front end.