I'm still interested in comments composition operators at http://haskell.org/haskellwiki/TypeComposition . Now I see that my ":.::" is what [1] calls "StaticArrow".

Mainly, I'd like to hear thoughts on how to make an arrow out of a functor & arrow, with the functor on the inside. My attempt is called " ::.:" on the wiki page.

    newtype (
(~>) ::.: f) a b = TT_T {
runTT_T :: f a ~> f b}

As mentioned in the comments, my Arrow definition isn't really satisfactory. Is there an arrow that corresponds to this sort of composition?

Thanks, - Conal

On 3/8/07, Conal Elliott <conal@conal.net> wrote:

I made a first pass at a module of type compositions with some instances at http://haskell.org/haskellwiki/TypeComposition and would love to get comments & suggestions.

Is there an existing process for library proposals & discussions?

Cheers, - Conal

On 2/21/07, Ross Paterson < ross@soi.city.ac.uk> wrote:
[redirecting to libraries]
On Wed, Feb 21, 2007 at 04:23:50PM -0800, Conal Elliott wrote:
> Is the composition instance of Control.Applicative defined somewhere? I see
> it in the McBride & Paterson paper [1], but not in the library docs [2].
> I'd rather pull it in from a library than (re)define it myself.
>
> [1] http://www.soi.city.ac.uk/~ross/papers/Applicative.pdf
> [2]
> http://www.haskell.org/ghc/docs/latest/html/libraries/base/Control-Applicative.html

It's not defined in the libraries. The type (and the identity functor)
should probably go in the module that defines Functor (currently
Control.Monad) with a Functor instance, and an Applicative instance
in Control.Applicative.

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