echo_bad_2.idr

echo : IO ()
echo = loop (const True) where
  loop : (String -> Bool) -> IO ()
  loop isDifferent = do           -- `isDifferent` refers to the previous string
    putStr "in> "
    l <- getLine
    when (l /= "quit") $ do
      when (isDifferent l) $      -- If the string is different from the previous
        putStrLn ("out> " ++ l)   -- Echo the string in standard output
      loop (/= l)                 -- Track the last read string