Adding swap/compose functions to Data.Tuple and Data.Function

[Edward Kmett]

On Tue, Nov 20, 2012 at 2:14 PM, John Wiegley <johnw at fpcomplete.com> wrote:

> Moving discussion from http://hackage.haskell.org/trac/ghc/ticket/7435:
>
> I propose adding the following three functions to Data.Tuple and
> Data.Function, respectively:
>
>     swap :: (a,b) -> (b,a)
>     swap = snd &&& fst
>
>
Data.Tuple already contains swap.

Fairly obvious, but strangely missing.
>
>     compose :: [(a -> a)] -> a -> a
>     compose = foldr (.) id
>
>     composeM :: [(a -> m a)] -> a -> m a
>     composeM = foldr (<=<) return
>

I would actually consider these to fall beneath the "Fairbairn threshold".

The composition of them is obvious, and the suggested names already exist
commonly in a lot of third party code for all sorts of purposes.

The pain of adoption plus the annoyance of trying to find them exceeds, to
me, the utility of adding them.

-Edward
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