"Andre W B Furtado"
For example, suppose function doSomeStuffWith returns its own parameter. Using a 1.5MB file in this case, the Haskell program ends in almost 5 seconds, while the C program ends in less than 0.5 seconds... Is my Haskell program too bad implemented? (I'm using GHC 4.08-1 under a Windows 98 platform.)
I indeed think that your Haskell program is inefficient and is not a translation of your C program. It reverses a huge string, which takes not only execution time but also garbage collection time and memory, which entails even more time for OS overhead and swapping out other things in the physical memory. (Many programmers complain "my linear-time algorithm takes just 1 second on a 100M list, so why is it taking 5 seconds on a 200M list?" They forget that because of issues such as cache locality and virtual memory, their computers do not scale.) I am wondering that if doSomeStuffWith is pure-functional, why are you writing and using copyFile instead of just using map? I mean: main :: IO () main = do bmFile <- openFileEx "in.txt" (BinaryMode ReadMode) bmString <- hGetContents bmFile writeFile "out.txt" (map doSomestuffWith bmString) hClose bmFile Because both hGetContents and map are lazy and use O(1) memory, this program behaves exactly as your C program plus occasional garbage collections that don't hurt too much. In partcular, the OS will see no difference (although the cache does).