I'm not a huge fan of (.:), but you insist on adding it, please generalize it to fmap.fmap. (.:) :: (Functor f, Functor g) => (a -> b) -> f (g a) -> f (g b) This subsumes the other use case. -Edward On Tue, Aug 14, 2012 at 5:32 AM, David McGillicuddy wrote:

What about (.:)*? Just looking at Hayoo quickly, at least half a dozen libraries seem to have defined it and it's a permanent feature on lambdabot.

*(.:) :: (c -> d) -> (a -> b -> c) -> a -> b -> d (.:) = (.) (.) (.)

David

On Tue, Aug 14, 2012 at 7:54 AM, Simon Hengel wrote:

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On Mon, Aug 13, 2012 at 10:31:19PM -0400, Tom Murphy wrote:

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It would be great to have maybeRead in base in time for the next Haskell Platform release. There's been talk about including it several times, but it's remained as a utility function in other libraries (Network.CGI, for example, if I'm remembering right).

It's in base-4.6.0.0, but it's called readMaybe (personally, I don't like that name, but I guess it's for consistency with readEither).

Cheers, Simon

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This is part of why I'm not a fan of (.:) in the first place, but trying to generalize through Category doesn't offer anything here. Sent from my iPad On Aug 16, 2012, at 7:16 AM, Twan van Laarhoven wrote:

On 15/08/12 19:02, Edward Kmett wrote:

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I'm not a huge fan of (.:), but you insist on adding it, please generalize it to fmap.fmap.

(.:) :: (Functor f, Functor g) => (a -> b) -> f (g a) -> f (g b)

This subsumes the other use case.

For the love of Categories, please don't go down this road. fmap is not the proper generalization of (.).

Twan

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