Andre W B Furtado writes:
:
| copyFile :: String -> String -> IO String
| copyFile [] s = return (reverse s)
| copyFile (a:as) s = copyFile as ( (doSomeStuffWith a):s)
:
| 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.)
You've used an accumulating parameter (s) and then reversed it once
you reach the end of the input. The time cost for this is still O(n)
where n is the length of the input, but the space cost is O(n) in your
Haskell program and O(1) in your C program, so perhaps the Haskell
version's having to spend time enlarging its heap?
Here's an O(n) time, O(1) space version of copyFile:
copyFile = return . map doSomeStuffWith
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