[Haskell-cafe] Slow IO or bad code?

[Lutz Donnerhacke]

* Vimal wrote:
>>> Beginning of CODE
> loop t function
>  | t == 1 = do function
>  | otherwise = do { function; loop (t - 1) function }
>
> prod [] [] = 0
> prod (a:as) (b:bs) = a*b + prod as bs

prod = sum . zipWith (*)

> to_int :: [String] -> [Integer]
> to_int [] = []
> to_int (x:xs) = (read x) : to_int xs

This is the slow part. Prelude.read ist really slow.

Futhermore use the recusion pattern again:
to_int = map read

> doit = do
>   n <- getLine
>   a <- getLine
>   b <- getLine
>   let la = to_int (words a);
>       lb = to_int (words b); in
>     print (prod la lb)

What is n used for?