Answer Happy

Given this code
-- function to convert from number to list of digits
toDigits :: Integer -> [Integer]
toDigits n
| n < 10 = [n]
| otherwise = (toDigits (n `div` 10)) ++ [n `mod`10]
-- function to do the same bu tin reverse
toDigitsReverse :: Integer -> [Integer]
toDigitsReverse n = reverse (toDigits n)
-- function to help double every other element of list
doubleDigitsHelper :: [Integer] -> Integer ->[Integer]
doubleDigitsHelper l t
| l == [] = []
| t == 0 = [head l] ++ (doubleDigitsHelper (drop 1l) 1)
| t == 1 = [2*(head l)] ++ (doubleDigitsHelper(drop 1 l) 0)
-- function to double every other element
doubleDigits :: [Integer] -> [Integer]
doubleDigits l = reverse (doubleDigitsHelper (reverse l) 0)
-- function to return sum of digits of a number
sumOfDigits :: Integer -> Integer
sumOfDigits n
| n < 10 = n
| otherwise = (sumOfDigits (n `div` 10)) + (n`mod` 10)
-- function to get sum of digits and then sum of list
totalDigits :: [Integer] -> Integer
totalDigits [] = 0
totalDigits (l:ls) = (sumOfDigits l) + (totalDigits ls)
-- combine all the above functions to get the requiredalgorithm
verify :: Integer -> Bool
verify n =
if ((totalDigits (doubleDigits (toDigits n)))`mod` 10) == 0
then True
else False
How does each function precisely work?(In as much detailsas possible)