Paul Moore writes:
It would be interesting to see standalone code for wcIOB (where you're allowed to assume that any helpers you need, like your block IO library, are available from the standard library). This would help in comparing the "obviousness" of the two approaches.
A simple version of the program -- which doesn't need any 3rd party modules to compile -- is attached below. My guess is that this approach to I/O is quite obvious, too, if you have experience with system programming in C. IMHO, the main point of the example in the article is that wc :: String -> (Int, Int, Int) wc file = ( length (lines file) , length (words file) , length file ) is a crapy word-counting algorithm. I'm not sure whether conclusions about functional programming in general or even programming in Haskell can be derived from this code. Most people seem to have trouble with lazy-evaluation, first of all. Peter -- Compile with: ghc -O2 -funbox-strict-fields -o wc wc.hs module Main ( main ) where import System.IO import Foreign type Count = Int data CountingState = ST !Bool !Count !Count !Count deriving (Show) initCST :: CountingState initCST = ST True 0 0 0 wc :: Char -> CountingState -> CountingState wc '\n' (ST _ l w c) = ST True (l+1) w (c+1) wc ' ' (ST _ l w c) = ST True l w (c+1) wc '\t' (ST _ l w c) = ST True l w (c+1) wc _ (ST True l w c) = ST False l (w+1) (c+1) wc _ (ST False l w c) = ST False l w (c+1) bufsize :: Int -- our I/O buffer size bufsize = 4096 type IOHandler st = Ptr Word8 -> Int -> st -> IO st countBuf :: IOHandler CountingState countBuf _ 0 st@(ST _ _ _ _) = return st countBuf ptr n st@(ST _ _ _ _) = do c <- peek ptr let st' = wc (toEnum (fromEnum c)) st countBuf (ptr `plusPtr` 1) (n - 1) st' loop :: Handle -> Int -> IOHandler st -> st -> IO st loop h n f st' = allocaArray n (\ptr' -> loop' ptr' st') where loop' ptr st = st `seq` do rc <- hGetBuf h ptr n if rc == 0 then return st else f ptr rc st >>= loop' ptr main :: IO () main = do ST _ l w c <- loop stdin bufsize countBuf initCST putStrLn . shows l . (' ':) . shows w . (' ':) $ show c