On Wed, Feb 17, 2010 at 16:48, Stephen Tetley wrote:

On 17 February 2010 15:41, Mike Dillon <mike@embody.org> wrote:
> That signature is the `oo` "specs" combinator in Data.Aviary:

Nice!

I wouldn't recommend writing code that depends on Data.Aviary, but
some of the combinators are often worth copy/pasting out of it.

On the contrary, I think the specs combinators and perhaps others in Data.Aviary (probably not Data.Aviary.*) have potential. We could even generalize oo and the others to categories and add it to Control.Category (which is, after all, looking rather empty).

import Control.Category
import Prelude hiding ((.))

-- oo :: (c -> d) -> (a -> b -> c) -> a -> b -> d
oo :: (Category cat) => cat c d -> (a -> cat b c) -> a -> cat b d
oo = (.) . (.)

-- ooo :: (d -> e) -> (a -> b -> c -> d) -> a -> b -> c -> e
ooo :: (Category cat) => cat d e -> (a -> b -> cat c d) -> a -> b -> cat c e
ooo = (.) . (.) . (.)

-- oooo :: (e -> f) -> (a -> b -> c -> d -> e) -> a -> b -> c -> d -> f
oooo :: (Category cat) => cat e f -> (a -> b -> c -> cat d e) -> a -> b -> c -> cat d f
oooo = (.) . (.) . (.) . (.)

Is it necessary? Maybe not.

I'm guessing that the names oo, etc. do not have a commonly accepted meaning, so I like them. I'd like to have a module (e.g. Control.Pointfree) containing these and other useful general combinators from the community.

Sean