Example why you should avoid unsafe functions like `read`, or at least be careful.

script.hs

#!/usr/bin/env runhaskell
-- run as script to get correct buffering behavior
-- >>> chmod +x ./script.hs
-- >>> ./script.hs
module Main where

import Control.Exception

example :: IO Int
example =
  prompt `catch` handler -- exception thrown by `read` escapes catch
  -- (prompt >>= evaluate) `catch` handler -- force evaluation so exception cannot escape
  -- notice that `evaluate` only evaluates to WHNF. If you have unevaluated thunks inside 
  -- of that the exception still might escape our `catch`.
  where
    prompt :: IO Int
    prompt = read <$> (putStr "> " *> getLine)

    handler :: SomeException -> IO Int
    handler _ = do
      putStrLn "ERROR: invalid input"
      example

main :: IO ()
main = print =<< example