[GHC] #5438: Wrong result for element check

[GHC]

#5438: Wrong result for element check
----------------------------------+-----------------------------------------
    Reporter:  daniel.is.fischer  |       Owner:                             
        Type:  bug                |      Status:  new                        
    Priority:  normal             |   Component:  Data Parallel Haskell      
     Version:  7.0.4              |    Keywords:                             
    Testcase:                     |   Blockedby:                             
          Os:  Unknown/Multiple   |    Blocking:                             
Architecture:  Unknown/Multiple   |     Failure:  Incorrect result at runtime
----------------------------------+-----------------------------------------
 On the [http://haskell.org/pipermail/beginners/2011-August/008422.html
 beginners] list, Luca Ciciriello reported that
 {{{
 {-# LANGUAGE PArr #-}
 {-# OPTIONS -fdph-seq #-}

 module Main where

 import Control.Parallel
 import GHC.PArr

 parArr :: [:String:]
 parArr = [: "1", "2", "3", "4" :]

 isElement :: String -> Bool
 isElement x = x `elemP` parArr

 main :: IO ()
 main = do
           putStrLn $ (show . isElement) "5"
 }}}
 prints True. Obviously it should print False. I've replicated the
 behaviour with 7.0.4 and 6.10.4 on 64-bit linux (Luca tested on Mac and
 Windows).

 As far as I can tell, elemP no longer exists in dph, so I had to modify to
 test with HEAD, and
 {{{
 {-# LANGUAGE ParallelArrays #-}
 {-# OPTIONS -fdph-seq #-}

 module Main where

 import GHC.PArr
 import Data.Array.Parallel

 parArr :: [:String:]
 parArr = [: "1", "2", "3", "4" :]

 isElement :: String -> Bool
 isElement x = x `elemP1` parArr
   where
     elemP1 :: Eq a => a -> [:a:] -> Bool
     elemP1 v ar = lengthP (filterP (== v) ar) /= 0

 main :: IO ()
 main = do
           putStrLn $ (show . isElement) "5"
 }}}
 also prints True with HEAD, but prints False with 6.10.4 and 7.0.4 (with
 the necessary modifications, !ParallelArrays -> PArr, don't import
 Data.Array.Parallel).

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5438>
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