Ticket #188: freezeex.2.hs

{-# OPTIONS -fglasgow-exts  #-}

module Main where

import IO
import Array
import Monad
import Control.Monad.ST(runST,ST)
import Data.Array.ST(STArray,writeArray,unsafeFreeze,thaw,unsafeThaw)



prog4:: (Array Int Int) -> Int -> ST s (Array Int Int)
prog4 a i = do am <- (unsafeThaw a:: ST s (STArray s Int Int))
               --am <- (thaw a:: ST s (STArray s Int Int)) 
               writeArray am i (42+i)
               af <- unsafeFreeze am
               return af

default_len = 5000

main ::IO ()
main = do lens <- getLine
          let len = if lens=="" then default_len else (read lens)
          let a = listArray (0,len) [1..]
          let b = runST (do foldM prog4 a [1..(len-2)])
          putStr $ show [b!i | i <-[1..10]]
          putStr $ show [b!(len-i) | i <-[1..10]]
          putStr "\n"
{- 
command line:  
echo 5200 | ./freezeex

ghc 5.04.1 -O
  8000 result
  8500 scavenge error
  9000 seg. fault

ghc 6.0.1, unoptimised
  4000 result, 6'26" on Xeon 2.4
  5230 result, 18'11"

ghc 6.0.1 -O
  -5218 result
  5219-5221 result, segm. fault
  5222- segm. fault

-O2 same as -O
-}