[Haskell-cafe] Re: what is inverse of mzero and return?
jules at jellybean.co.uk
Tue Jan 25 09:29:12 EST 2005
On 25 Jan 2005, at 13:20, Keean Schupke wrote:
> f = getChar >>= (\a -> if a == "F" then mzero else return a)
> In this case if the LHS returns "F" the LHS should not have been
> run... this contradicts itself, so
> this is a non option I guess.
Good paradox. That is what is upsetting me, too.
> Acutally looking at GHC CVS libraries, there is not a definition for
> MonadPlus on the state or IO
It's in Control.Monad.Error. Not documented though.
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