[Haskell-cafe] foldr (.) id
tonymorris at gmail.com
Sat Oct 27 01:01:37 CEST 2012
It's the Endo monoid.
?> :t ala Endo foldMap -- see newtype package
ala Endo foldMap :: Foldable t => t (a -> a) -> a -> a
?> ala Endo foldMap [(+1), (*2)] 8
?> :i ala
(Newtype n o, Newtype n' o') =>
(o -> n) -> ((o -> n) -> b -> n') -> b -> o'
-- Defined in Control.Newtype
On 27/10/12 04:41, 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.
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
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