sicp 1.17 in haskell

sicp1.17.hs

-- ...
-- ...
-- [Assume your language doesn't have a multiplication function or
-- table. Given `double` and `half` functions,] design a
-- multiplication procedure that uses a logarithmic number of steps.

double :: Integer -> Integer
double x = x + x

halve :: Integer -> Integer
halve x = x `div` 2

m :: Integer -> Integer -> Integer
m x y
    | y == 0 = 0
    | odd y = x + m x (y - 1)
    | otherwise = m (double x) (halve y)