6.8.1. Multi-parameter type classes — Glasgow Haskell Compiler 9.14.0.20251028 User's Guide

# 6.8.1. Multi-parameter type classes

MultiParamTypeClasses
  Implies:

    `ConstrainedClassMethods`

  Implied by:

    `FunctionalDependencies`

  Since:

    6.8.1

  Status:

    Included in `GHC2024`, `GHC2021`

  Allow the definition of typeclasses with more than one parameter.

Multi-parameter type classes are permitted, with extension `MultiParamTypeClasses`. For example:

    class Collection c a where
        union :: c a -> c a -> c a
        ...etc.