{- Merge two sorted lists -}
merge (x:xs) (y:ys)
  | x < y = x: merge xs (y:ys)
  | x > y = y: merge (x:xs) ys
  | x == y = x: merge xs ys

merge [] ys = ys
merge xs [] = xs

{-- Generic Hamming sequence on a list of factors. --}
genHam :: [Integer]->[Integer]
genHam [] = []
genHam (x:xs) = out
 where
   out = merge ( 1: map (*x) out) (genHam xs)

{- Usage:
take 10 (genHam [2,3,5])
-}