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

[Thomas Davie]

On 14 Apr 2010, at 09:25, Ashley Yakeley wrote:

> 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.

It isn't?

fPrelude> fmap id (undefined :: IO ())
*** Exception: Prelude.undefined

Bob