import System.IO.Unsafe ( unsafePerformIO )
import Data.List ( sort )
import System.Environment ( getArgs )
import Text.Read ( readMaybe )

-- what it IO worked as any other thing in Haskell?
doLog :: Show a => a -> a
doLog x = unsafePerformIO $ putStr ("<" ++ show x ++ ">") >> pure x

numlist, numlist2 :: [Int]
numlist = [doLog 1, doLog 2, doLog 3, doLog 4, doLog 5, doLog 1, doLog 4]
numlist2 = [doLog 4, doLog 2]

results = [ "sum: " ++ show (sum numlist)
          , "foldr: " ++ show (foldr (+) 0 numlist)
          , "reverse: " ++ show (reverse numlist)
          , "sort: " ++ show (sort numlist)
          , "(!! 2): " ++ show (numlist !! 2)
          , "numlist2: " ++ show numlist2
          ]

main = getArgs >>= \a -> putStr . unlines $ case head' a >>= readMaybe of
          Just x -> [results !! x]
          Nothing -> results


head' :: [a] -> Maybe a
head' []    = Nothing
head' (x:_) = Just x