[Haskell-cafe] foldr (.) id

Nick Vanderweit nick.vanderweit at gmail.com
Sat Oct 27 00:27:39 CEST 2012

Funny, I was thinking this morning about using something like this to convert 
to/from Church numerals:

church n = foldl (.) id . replicate n
unchurch f = f succ 0

I think it's a nice pattern.


On Friday, October 26, 2012 11:41:18 AM Greg Fitzgerald wrote:
> Hi Haskellers,
> I've recently found myself using the expression: "foldr (.) id" to compose
> a list (or Foldable) of functions.  It's especially useful when I need to
> map a function over the list before composing.  Does this function, or the
> more general "foldr fmap id", defined in a library anywhere?  I googled and
> hoogled, but no luck so far.
> Thanks,
> Greg

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