[Haskell-cafe] Where is the pairing-with-monoid monad instance?
leather at cs.uu.nl
Wed Jan 11 09:11:31 CET 2012
On Wed, Jan 11, 2012 at 03:23, Conal Elliott wrote:
> Is the standard pair-with-monoid monad instance in some standard place? I
> see the Applicative instance in Control.Applicative, and the
> pair-with-monoid Functor instance in Control.Monad.Instances, and the (->)
> e and Either e monad instances also in Control.Monad.Instances.
> I'm looking for something like
> instance Monoid o => Monad ((,) o) where
> return a = (mempty,a)
> (o,a) >>= f = (o `mappend` o', b)
> where (o',b) = f a
> Where is it hiding from me?
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