Re: [Haskell-cafe] Re: what is inverse of mzero and return?

[Keean Schupke]

Jules Bean wrote:
It's in Control.Monad.Error. Not documented though.
Jules
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...

   Keean
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