module Main where import System.Environment import Text.Read data EvenOdd = Even | Odd deriving (Show) isEvenOdd :: Int -> EvenOdd isEvenOdd x | x `mod` 2 == 0 = Even | otherwise = Odd headMaybe :: [a] -> Maybe a headMaybe  = Nothing headMaybe (x:xs) = Just x main :: IO () main = do args <- getArgs let x = headMaybe args case x >>= readMaybe of Nothing -> putStrLn "Usage: please input a number" Just x -> putStrLn $ show $ isEvenOdd x
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Note: The solution shown above is the current solution in the Sample Programs repository as of Nov 16 2018 11:15:37. The solution was first committed on Nov 16 2018 01:28:55. As a result, documentation below may be outdated.
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