[Haskell-cafe] Monad fold

[Lyndon Maydwell]

Yep. I was backstabbed by ghci seemingly having no issue with my definition
when I asked for the type.


On Tue, Apr 16, 2013 at 9:49 PM, Tom Ellis <
tom-lists-haskell-cafe-2013 at jaguarpaw.co.uk> wrote:

> On Tue, Apr 16, 2013 at 01:53:19PM +0100, Oliver Charles wrote:
> > On 04/16/2013 01:47 PM, Lyndon Maydwell wrote:
> > >You could do:
> > >
> > >runKleisli . mconcat . map Kleisli :: Monoid (Kleisli m a b) => [a
> > >-> m b] -> a -> m b
> > >
> > >Would that work for you?
> > I can't find an instance for Monoid (Kleisli m a b) in `base`, so
> > presumably the author would also have to write this instance? If so
> > - would that really be any different to using that fold?
>
> It doesn't make sense anyway.  It would have to be "Kleisli m a a" which
> would presumably require a newtype.
>
> Tom
>
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