[Haskell-cafe] Newtype derivation understanding problem
k-bx at k-bx.com
Thu Jul 31 11:04:30 UTC 2014
Yes, sorry! I also for some reason added "deriving MonadCatchIO" which is
not there :) I needed to see it's not derived, that's why I should do a
search for it.
On Thu, Jul 31, 2014 at 2:00 PM, Mikael Brockman <mbrock at goula.sh> wrote:
> Konstantine Rybnikov <k-bx at k-bx.com> writes:
> > Excuse me if the question is silly.
> > Thought this MonadCatchIO will be removed in next version of snap,
> > current version has it and I can't understand this derivation: 
> > L.Lensed seems like just a newtype wrapper around a function , and
> > there is no instance of MonadCatchIO for a function.
> > How is it derived?
> You probably just missed it, but there's a MonadCatchIO instance for
> L.Lensed, and so the derived instance for Handler is trivial.
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