[Haskell-cafe] Re: Numeric type classes

Ashley Yakeley ashley at semantic.org
Wed Sep 13 18:43:28 EDT 2006

Aaron Denney wrote:

> I know of no good way to express that a given data type obeys the
> same interface two (or more) ways.

The best approach here is to use data structures instead of classes:

data Monoid a = MkMonoid
   monoidNull :: a,
   monoidFunc :: a -> a -> a

Ashley Yakeley

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