listsum.hs

listsum :: Num a => [a] -> a
listsum [] = 0
listsum (x:xs) = x + listsum xs

main :: IO ()
main = print $ listsum [1..5]

mykth.hs

mykth :: (Ord n, Num n) => [a] -> n -> a
mykth [] _     = error "Invalid argument"
mykth (x:_)  1 = x
mykth (_:xs) k =
    if k < 1
    then error "Index is out of boundaries"
    else mykth xs (k-1)

mylast.hs

mylast :: [a] -> a
mylast = head . reverse

main :: IO ()
main = do
    print $ mylast [1..4]
    print $ mylast "rajanikant"

secondlast.hs

secondlast :: [a] -> a
secondlast xs = case reverse xs of
    (_:x:_) -> x
    _       -> error "List is too short"

main :: IO ()
main = print $ secondlast [1..5]