#3487: Data.ByteString.Lazy.elemIndices returns wrong results
-----------------------------+----------------------------------------------
Reporter: nwn | Owner:
Type: bug | Status: new
Priority: normal | Component: libraries/base
Version: 6.10.4 | Severity: normal
Keywords: | Testcase:
Os: Unknown/Multiple | Architecture: x86
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elemIndices for Lazy ByteString returns wrong results occasionally for
huge input.
{{{
-- lei.hs
import qualified Data.ByteString.Lazy as L
import Control.Monad
main = do
n <- fmap (length . L.elemIndices 10) L.getContents
putStrLn (show n)
}}}
{{{
$ ghc --make lei
[1 of 1] Compiling Main ( lei.hs, lei.o )
Linking lei ...
$ yes | head -1000000 | ./lei
1000000
$ yes | head -1000000 | ./lei
999992
$ yes | head -1000000 | ./lei
999960
$ yes | head -1000000 | ./lei
1000000
$ yes | head -1000000 | ./lei
999976
}}}
Without getContents, elemIndices works fine.
{{{
import qualified Data.ByteString.Lazy as L
import System.Environment
main = do
n <- fmap (read . head) getArgs
let cs = L.pack . take (2*n) . cycle $ [48,10]
ps = L.elemIndices 10 cs
print (length ps)
}}}
{{{
$ ghc --make lei2.hs
[1 of 1] Compiling Main ( lei2.hs, lei2.o )
Linking lei2 ...
$ ./lei2 1000000
1000000
$ ./lei2 1000000
1000000
}}}
So I think there is a problem about bytestring IO.
And I heard this isn't reproduced in Windows' command prompt.
This ticket is based on [http://www.sampou.org/cgi-bin/w3ml.cgi/haskell-
jp/msg/381 a thread of haskell-jp].
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3487>
GHC <http://www.haskell.org/ghc/>
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