[GHC] #1131: newArray_ allocates an array full of garbage

[GHC]

#1131: newArray_ allocates an array full of garbage
-------------------------------+--------------------------------------------
    Reporter:  igloo           |       Owner:         
        Type:  bug             |      Status:  new    
    Priority:  normal          |   Milestone:  6.8    
   Component:  libraries/base  |     Version:  6.6    
    Severity:  normal          |    Keywords:         
  Difficulty:  Unknown         |    Testcase:         
Architecture:  Unknown         |          Os:  Unknown
-------------------------------+--------------------------------------------
In http://www.haskell.org/pipermail/haskell-cafe/2006-December/020115.html
 Stefan O'Rear points out that newArray_ allocates an array full of
 garbage. For ST this violates referential transparency, and it presumably
 also means we are leaking information we shouldn't.

 For example, running

 {{{
 import Control.Monad.ST
 import Data.Array.ST
 import Data.Array
 import System.Mem

 tickle :: Int
 tickle = runST (do {
      x <- newArray_ (0,100) ;
      (readArray :: STUArray s Int Int -> Int -> ST s Int) x 3
    })

 main :: IO ()
 main = do print $ length (replicate 100000 'a')
           performGC
           print tickle
 }}}

 produced

 {{{
 $ ./q
 100000
 46912506425344
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1131>
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