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@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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