mySum :: [Int] -> Int
mySum [] = 0
mySum (a:as) =  a + mySum as

myProduct :: [Int] -> Int
myProduct [] = 1
myProduct (a:as) =  a * myProduct as

myPow :: Int -> Int -> Int
myPow b e
    | e == 0 = 1
    | e == 1 = b
    | otherwise = b * myPow b (e - 1)

size :: [Int] -> Int
size [] = 0
size (a:as) = 1 + size as

nesimo :: Int -> [Int] -> Int
nesimo n (a:as)
    | n == 0 = a
    | otherwise = nesimo (n - 1) as

inverter :: [Int] -> [Int]
inverter [] = []
inverter (a:as) = inverter as ++ (a:[])

main :: IO ()
main = do
    putStrLn $ "Soma dos elementos da lista: " ++ show (mySum [1, 2, 3, 4, 5])
    putStrLn $ "Produto dos elementos da lista: " ++ show (myProduct [1, 2, 3, 4, 5])
    putStrLn $ "Tamanho da lista: " ++ show (size [1, 2, 3, 4, 5])
    putStrLn $ "Potenciacao b ^ e: " ++ show (myPow 2 1)
    putStrLn $ "Nesimo elemento da lista (2): " ++ show (nesimo 2 [3, 4, 7, 9, 12])
    putStrLn $ "Inverter lista: " ++ show (inverter [1, 2, 3, 4, 5])