Data.Either.partitionEithers is not lazy enough
Data.Either.partitionEithers gives a stack overflow for long or infinite lists.
Change
partitionEithers :: [Either a b] -> ([a],[b])
partitionEithers = foldr (either left right) ([],[])
where
left a (l, r) = (a:l, r)
right a (l, r) = (l, a:r)
to
partitionEithers :: [Either a b] -> ([a],[b])
partitionEithers = foldr (either left right) ([],[])
where
left a ~(l, r) = (a:l, r)
right a ~(l, r) = (l, a:r)
to make it lazy enough.
Example:
Data.Either> let fun k = case gcd k 15 of { 3 -> Left "Fizz"; 5 -> Left "Buzz"; 15 -> Left "FizzBuzz"; _ -> Right k }
Data.Either> take 10 . snd . partitionEithers $ map fun [1 .. 2*10^6 :: Integer]
*** Exception: stack overflow
Data.Either> take 10 . snd . lpartitionEithers $ map fun [1 :: Integer .. ]
[1,2,4,7,8,11,13,14,16,17]
Trac metadata
Trac field | Value |
---|---|
Version | 6.10.4 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | libraries/base |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |