--
sumCustom :: (Num a) => [a] -> a
sumCustom [] = 0
sumCustom (x:xs) = x + sumCustom xs
--
(<+>) :: [a] -> [a] -> [a]
(<+>) [] xs = xs
(<+>) (x:xs) ys = x : (xs <+> ys)
--
reverseCustom :: [a] -> [a]
reverseCustom [] = []
reverseCustom (x:xs) =  reverseCustom xs <+> [x]
--
initCustom :: [a] -> [a]
initCustom [] = error "Empty list"
initCustom (x:[]) = []
initCustom (x:xs) = x: initCustom xs
--
lastCustom :: [a] -> a
lastCustom [] = error "Empty list"
lastCustom (a:[]) = a
lastCustom (x:xs) = lastCustom xs
--
initsCustom :: [a] -> [[a]]
initsCustom [] = error "Empty list"
initsCustom (x:[]) = [[x]]
initsCustom (x:xs) = initsCustom(initCustom(x:xs)) <+> [x:xs]
--
tailsCustom :: [a] -> [[a]]
tailsCustom [] = error "Empty list"
tailsCustom (x:[]) = [[x]]
tailsCustom (x:xs) =   [x:xs] <+> tailsCustom(xs)
--