What type of scope does Haskell use?

let x = 10

let square x = x*x

import Data.IORef

main :: IO ()
main = do x <- newIORef 0         -- write 0 into x
          readIORef x >>= print   -- x contains 0
          let y = x
          readIORef y >>= print   -- y contains 0
          writeIORef x 42         -- write 42 into x
          readIORef y >>= print   -- y contains 42

x = 10

square x = x * x

square =  x -> x * x

foo x y = x * y
bar z = foo z z

y = x

type Function = Double -> Double

evens = 0 : map (+1) odds
odds  = map : (+1) evens

let x = 2 * n
    x = x + 1   -- watch out!

import Data.IORef

main :: IO ()
main = do x <- newIORef 0         -- write 0 into x
          readIORef x >>= print   -- x contains 0
          let y = x
          readIORef y >>= print   -- y contains 0
          writeIORef x 42         -- write 42 into x
          readIORef y >>= print   -- y contains 42