ghci> x <- readFile "foo.txt"
  ghci> let y = read x :: [Int]
  ghci> :t y
  y :: [Int]

x <- readFile "foo.txt"

example = do
  x <- readFile "foo.txt"
  let y = read x :: [Int]
  return y

readFoo = do
    x <- readFile "foo.txt"
    let y = read x :: [Int]
    return y

a -> IO a