[Haskell-cafe] Monad fold

[Roman Cheplyaka]

Right. See also this discussion:
http://www.haskell.org/pipermail/libraries/2009-July/012106.html

Roman

* Tom Ellis <tom-lists-haskell-cafe-2013 at jaguarpaw.co.uk> [2013-04-16 14:49:48+0100]
> 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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