[Haskell-cafe] Fast code question

[Don Stewart]

Can you use the bytestring csv parser (or convert it into a pretty
printer?)

bartek:
> Hi Folks,
> 
> I had to transform Packed Decimal file into csv format (does anybody here know 
> what this Mainframe format is?).  Because of the file size I could not do 
> this on mainframe directly. So I've created simply program using ByteString. 
> Generally I'm happy with my solution: pgm processes arroud 2MB/s on my pc, so 
> my 3GB file was transformed in reasonable 30 min time.
> 
> My question is: how to do this faster?
> 
> {code}
> module Main 
> where 
>  
> import qualified Data.ByteString.Lazy as B 
>  
> main =  B.getContents >>= myPrint . myConcat . B.unpack 
                                                  ^^^^^^^^^^^^^^^^^^^^^
                                                    That looks bad.

>  
> myConcat = myConcat' 0 
>  
> myConcat' :: (Integral a) => Integer -> [a] -> [Integer] 
> myConcat'  _  [] = [] 
> myConcat' acc (x:xs) = case x `mod` 16 of 
>                 12 -> (10*acc + (restOf . fromIntegral) x) : myConcat' 0 xs 
>                 13 -> ((-10)*acc + (restOf . fromIntegral) x) : myConcat' 0 xs 
>                 15 -> (10*acc + (restOf . fromIntegral) x) : myConcat' 0 xs 
>                 10 -> fail $ show acc
>                 11 -> fail $ show acc
>                 14 -> fail $ show acc
>                  v  -> myConcat' (100*acc + (numberOf . fromIntegral) x) xs 
>          where restOf n = (n - 12) `div` 16 
>                numberOf n = n - 6 * (n `div` 16) 
>  
> myPrint [] = return () 
> myPrint xs = mapM_ myShow (take 14 xs) >> putStrLn "" >> myPrint (drop 14 xs) 
>  
> myShow x = (putStr . show) x >> putStr ";"
> {code}
> 
> I knew that csv output had to be 14 fields per line.
> 
> Best,
> Bartek
> 
> 
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