I'm only start to learn Haskell.
I'm confused with std function and IO.

My solution (does not work):
main = do
   a <- getLine
   let b = sum map read words a // <- I try to use this functions
   putStrLn (show b)

let b = words a // work, but
let b = sum map (read::Int) words a //does not work

Where I wrong?

try this
let b str = sum (map (read :: String -> Int) (words str))
or this
let b str = sum (map read (words str)) :: Int
related info:
http://www.haskell.org/haskellwiki/Type_inference
http://www.haskell.org/tutorial/classes.html

Thank you very much :)