[Haskell-cafe] Where is the pairing-with-monoid monad instance?
conal at conal.net
Wed Jan 11 03:23:33 CET 2012
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?
Thanks, - Conal
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