length' [] = 0 length' (_:xs) = 1 + length' xs sum' [] = 0 sum' (x:xs) = x + sum' xs product' [] = 1 product' (x:xs) = x * product' xs take' _ [] = [] take' n _ | n < 1 = [] take' n (x:xs) = x : take' (n - 1) xs drop' _ [] = [] drop' n xs …