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

[Andreas Abel]

On 20.11.2012 20:14, John Wiegley 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

+1

> Fairly obvious, but strangely missing.
>
>      compose :: [(a -> a)] -> a -> a
>      compose = foldr (.) id
>
>      composeM :: [(a -> m a)] -> a -> m a
>      composeM = foldr (<=<) return
>
> This can be done with Endo, of course, but the result is awkward. The idiom of
> composing a list of endomorphisms occurs often enough that you can Google for
> it.

+0.5  (a bit in doubt whether these are common enough).



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