[Haskell-cafe] Re: instance Eq (a -> b)

Ashley Yakeley ashley at semantic.org
Wed Apr 14 04:25:47 EDT 2010

Thomas Davie wrote:
> Because we consider that the Functor laws must hold for all values in the type (including bottom).

This is not so for IO, which is an instance of Functor. "fmap id 
undefined" is not bottom.

Ashley Yakeley

More information about the Haskell-Cafe mailing list