wiki:MultiParamTypeClasses

Version 4 (modified by ross@…, 10 years ago) (diff)

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Multi-parameter type classes

See ExtensionDescriptionHowto for information on how to write these extension descriptions. Please add any new extensions to the list of HaskellExtensions.

Brief Explanation

Classes take one or more arguments, becoming relations between types.

References

Pros

  • offered by GHC and Hugs for years
  • express more interesting relationships, as in the two occurrences in the base package of the Haskell hierarchical libraries:
    class HasBounds a => IArray a e
    class (HasBounds a, Monad m) => MArray a e m
    
    The instances supplied do not overlap.

Cons