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Last active Oct 30, 2017
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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
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