This mail pretty much sums up the situation: http://www.haskell.org/pipermail/glasgow-haskell-bugs/2004-October/004389.ht ml This will be fixed in GHC 6.4. /Josef
-----Original Message----- From: libraries-bounces@haskell.org [mailto:libraries-bounces@haskell.org] On Behalf Of Lemming Sent: den 31 oktober 2004 18:37 To: libraries@haskell.org Subject: Data.List.partition on infinite lists
I encountered that the implementation of 'partition' in GHC 6.2.1 fails on infinite lists:
partition :: (a -> Bool) -> [a] -> ([a],[a]) partition p xs = foldr (select p) ([],[]) xs
select p x (ts,fs) | p x = (x:ts,fs) | otherwise = (ts, x:fs)
With the following definition we don't have this problem:
partition :: (a -> Bool) -> [a] -> ([a], [a]) partition _ [] = ([],[]) partition p (x:xs) = let (y,z) = partition p xs in if p x then (x : y, z) else (y, x : z)
Prelude> take 10 $ fst $ partition even [0..] [0,2,4,6,8,10,12,14,16,18] Prelude> take 10 $ snd $ partition even [0..] [1,3,5,7,9,11,13,15,17,19]
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