Well, playing with Haskell I have literally trasnlated my c++ program http://shootout.alioth.debian.org/u64q/program.php?test=fannkuchredux&lang=gpp&id=3and got decent performance but not that good in comparisonwith c++ On my machine Haskell runs 52 secs while c++ 30 secs.(There is Haskell entry that is fastest but unfortunately does not runs on test machine is on par with c++http://shootout.alioth.debian.org/u64q/program.php?test=fannkuchredux&lang=ghc&id=3)There is something which I have missing since programsare identical.Aa with previous entries you gurus here helped a lot in both helpand learning experience.I simply love Haskell ;)I plan to contribute this program as it is much faster than current runningentry http://shootout.alioth.debian.org/u64q/program.php?test=fannkuchredux&lang=ghc&id=2even if it is multithreaded and my is not. This is program: {-# LANGUAGE CPP, BangPatterns #-}{- The Computer Language Benchmarks Game http://shootout.alioth.debian.org/ contributed by Branimir Maksimovic -} import System.Environmentimport Text.Printfimport Data.Bits import qualified Data.Vector.Unboxed.Mutable as VMimport qualified Data.Vector.Generic.Mutable as VGimport qualified Data.Vector.Unboxed as V main = do n <- getArgs >>= readIO.head (checksum,maxflips) <- fannkuch n printf "%d\nPfannkuchen(%d) = %d\n" checksum n maxflips fannkuch n = do !perm <- V.unsafeThaw $ V.fromList [1..n] !tperm <- VG.new n !cnt <- VG.replicate n 0 let loop :: Int -> Int -> Int -> IO(Int,Int) loop !c !m !pc = do !b <- next_permutation perm n cnt if b == False then return (c,m) else do VM.unsafeCopy tperm perm !flips <- count_flips tperm 0 loop (c + (if pc .&. 1 == 0 then flips else -flips)) (max m flips) (pc+1) r <- loop 0 0 1 return r next_permutation :: VM.IOVector Int -> Int -> VM.IOVector Int-> IO(Bool)next_permutation !perm !n !cnt = do !i <- loop 1 if(i >= n) then return False else do !v <- VM.unsafeRead cnt i VM.unsafeWrite cnt i (v+1) return True where loop :: Int -> IO(Int) loop !i | i < n = do !tmp <- VM.unsafeRead perm 0 let rotate :: Int -> IO() rotate !j = if j >= i then do VM.unsafeWrite perm i tmp return () else do !v <- VM.unsafeRead perm (j+1) VM.unsafeWrite perm j v rotate (j+1) rotate 0 !v <- VM.unsafeRead cnt i if v >= i then do VM.unsafeWrite cnt i 0 loop (i+1) else return i | otherwise = return i count_flips :: VM.IOVector Int -> Int -> IO(Int)count_flips !tperm !flips = do !f <- VM.unsafeRead tperm 0 if f == 1 then return flips else do VG.reverse $ VM.unsafeSlice 0 f tperm count_flips tperm (flips+1)