On 1/7/06, Chris Kuklewicz
When you put "print (head p)" at then end, it keeps a reference to the whole list "p" which is your space leak. If you want to store the head of p, this *should* work:
main = do n <- getArgs >>= return . read . head let p = permutations [1..n] headOfP <- return (head p) mapM_ (putStrLn . concatMap show) $ take 30 p putStr $ "Pfannkuchen(" ++ show n ++ ") = " putStrLn . show $ foldl' (flip (max . steps 0)) 0 p print headOfP
The "headOfP" is computed as an IO action at that point in the program, so "headOfP" does not hold a reference to "p" as a whole.
Without having tried this I'd say that you should use Control.Excection.evaluate instead of 'return'. Or you could use 'seq'. I suspect that otherwise the 'head p' will not be evaluated until the last line and you will have the same problem as before. Cheers, /Josef