Honor cmdline argument outside Int range

say (Right x) = print x

say (Left x) = putStrLn x

sayNum :: Maybe Int -> IO ()

sayNum :: Maybe Integer -> IO ()

sayNum Nothing  = say `foldMap` fizzbuzz

sayNum (Just n) = say `foldMap` (take n fizzbuzz)

sayNum (Just n) = (say.fizzeval) `foldMap` [1 .. n]

parseArgs :: [String] -> IO (Maybe Int)

parseArgs :: [String] -> IO (Maybe Integer)

parseArgs args =

    if null args then pure Nothing else pure int

    where int = if null parsed || (not $ null $ snd $ head parsed)

                   then Nothing

                   else Just $ fst $ head parsed

                where parsed = reads $ head args :: [(Int, String)]

                where parsed = reads $ head args :: [(Integer, String)]

main :: IO ()

main = getArgs >>= parseArgs >>= sayNum