[Haskell-cafe] sum $ map f xs ... ghc-7.10 performance regression?
tkoster at gmail.com
Tue Dec 15 23:06:48 UTC 2015
On Tue, Dec 15, 2015 at 1:15 AM, Thomas Koster <tkoster at gmail.com> 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 <rf at rufflewind.com> wrote:
> According to the source code for base-4.8 (GHC 7.10), sum is
> specialized to GHC.List.sum for lists.
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
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