[Haskell-beginners] Functor question

Jason Dusek jason.dusek at gmail.com
Tue Nov 17 01:07:45 EST 2009

  Functor must be defined for all types -- not some restriction
  thereof (hence you see talk of indexed functors).

  Thus `fmap` needs to be typeable for any `a -> b` but the
  construcor `Moo` is only typeable at `a, b` such that we have
  both `Num a, Num b`.

Jason Dusek

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