On Mon, Feb 10, 2014 at 11:26 AM, Dominique Devriese <dominique.devriese@cs.kuleuven.be> wrote:
I disagree. Just think about the Ord type class.  A decidable order
relation for a type is definitely something I would consider a clear
semantical meaning, but different sensible instances can be defined
for many types...  The same thing goes for Eq or Monoid or MonadState
or...

Sure... but now you have to make sure everything agrees about it. The way you do this in Haskell is to give your custom instance a distinct type to go with it. (Now go look at the Sum and Product monoids).

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