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

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