[Haskell-cafe] Re: Kleisli composition operator
duncan.coutts at worc.ox.ac.uk
Sun Aug 3 11:09:46 EDT 2008
On Sun, 2008-08-03 at 14:52 +0000, Roly Perera wrote:
> > I'm obviously missing something basic here but I don't seem to be able to use
> > the >=> operator which is apparently defined in the Prelude and also in
> > Control.Monad.
> Sorry, I wasn't very clear in my original posting. What I meant to say is that
> the compiler seems to be unable to find a definition of >=>. I get the message:
> Not in scope: `>=>'
> My understanding is that I shouldn't need to import this at all by default, and
> that importing Control.Monad should also pick it up.
It's not in the Prelude but it is in Control.Monad in base version 3
and later. You're probably using an older GHC which has base version
You can define it locally:
-- | Left-to-right Kleisli composition of monads.
(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> (a -> m c)
f >=> g = \x -> f x >>= g
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