Re: [Haskell-cafe] Newtype derivation understanding problem

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. Thank you. On Thu, Jul 31, 2014 at 2:00 PM, Mikael Brockman wrote:

Konstantine Rybnikov 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: [0]

L.Lensed seems like just a newtype wrapper around a function [1], 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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