On Jan 7, 2006, at 11:56 AM, Chris Kuklewicz wrote:
This is all about lazy evaluation.
Actually, I understand about lazy evaluation. What I don't understand is the extent of variable bindings. If I desugar the code this far: main = do n <- getArgs >>= return . read . head main' n main' n = let p = permutations [1..n] in do mapM_ (putStrLn . concatMap show) $ take 30 p putStr $ "Pfannkuchen(" ++ show n ++ ") = " putStrLn . show $ foldl' (flip (max . steps 0)) 0 p 'p' is a variable bound by a normal 'let.' Why isn't 'p' kept around until the whole 'in' expression is evaluated? If it were, then I assume the GC would be obliged to copy everything it pointed to. In the original version, the author called 'permutations' twice and didn't create a variable binding. Cheers, David -------------------------------- David F. Place mailto:d@vidplace.com