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

Tue, 25 Jan 2005 06:47:22 -0800 

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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