[Haskell-cafe] Re: what is inverse of mzero and return?
k.schupke at imperial.ac.uk
Tue Jan 25 09:46:17 EST 2005
Jules Bean wrote:
> It's in Control.Monad.Error. Not documented though.
Ahh, so it is:
instance MonadPlus IO where
mzero = ioError (userError "mzero")
m `mplus` n = m `catch` \_ -> n
So, the author of this obviously subscribed to the view that
side-effects are not
counted when considering function identity...
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