+1. Or, for the friends of point-free programming, foldr f = fromMaybe (error "foldr1: empty structure") . foldr (\ x -> Just . maybe x (f x)) Nothing On 29.10.2014 20:08, David Feuer wrote:
We currently have (in Data.Foldable)
foldr1 :: (a -> a -> a) -> t a -> a foldr1 f xs = fromMaybe (error "foldr1: empty structure") (foldr mf Nothing xs) where mf x Nothing = Just x mf x (Just y) = Just (f x y)
and something similar for foldl1. This is strict in the entire spine, unlike the list version, because it has to get all the way to the end of the list before it starts laying down Justs. I propose we change this to the obvious:
foldr1 :: (a -> a -> a) -> t a -> a foldr1 f xs = fromMaybe (error "foldr1: empty structure") (foldr mf Nothing xs) where mf x r = Just $ case r of Nothing -> x Just y -> f x y
Since GHC 7.10.1 is fast approaching, I doubt we have the usual two weeks to discuss this, so please speak up as soon as you can if you have concerns.
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