make change -- http://stackoverflow.com/questions/17242480/determining-ways-of-splitting-change

gistfile1.hs

-- http://stackoverflow.com/questions/17242480/determining-ways-of-splitting-change

-- the author writes:
-- assumes the denominations are distinct. If they aren't, 
--    ((there will be some dupicates present in the result produced))

change :: (Num a, Ord a) => [a] -> a -> [[a]]
change ds@ ~(d:t) sum 
  | sum==0  = [[]] 
  | null ds  = []
  | otherwise = concat [map (d:) $ change ds $ sum-d | d <= sum] ++ change t sum

-- my comment:
-- `d` is either present in the change, or not. If it is, then we can take 
--  one `d` coin out of the change, so it must be possible to change (sum-d).