Re: [Haskell-cafe] sum $ map f xs ... ghc-7.10 performance regression?

15 Dec 2015

      On Tue, Dec 15, 2015 at 1:15 AM, Thomas Koster  wrote:
...
Phil, I think that was true in 7.8, but if I'm reading the haddocks
correctly, Data.List.sum = Data.Foldable.sum in 7.10, and
Data.Foldable.sum uses foldMap/foldr.
On 15 December 2015 at 19:11, Phil Ruffwind  wrote:
...
According to the source code for base-4.8 (GHC 7.10), sum is
specialized to GHC.List.sum for lists.
https://hackage.haskell.org/package/base-4.8.1.0/docs/src/Data.Foldable.html...
My mistake. I didn't read past this:

class Foldable t where
  foldMap f = foldr (mappend . f) mempty
  sum = getSum #. foldMap Sum

instance Foldable [] where
  foldr = List.foldr

--
Thomas Koster