Fergus Henderson
Basically, I'm wondering if I should avoid using the standard library \\,
If efficiency is a significant concern, and the lists involved may be long, yes, you should.
I'm not sure how to preserve the semantics, either. (\\) seems to delete the first occurence of every value in the second list. I first tried this (\\\) :: Ord a => [a] -> [a] -> [a] a \\\ b = setToList $ minusSet (mkSet a) (mkSet b) and while it's often what I want, it's clearly not the same thing. More accurate to build a frequency table with freq xs = addListToFM_C (+) emptyFM $ zip xs $ repeat 1 and traverse the input something like (untested): a \\\ b = let ft = freq b in delf ft b delf ft (x:xs) = case lookupFM ft x of Nothing -> x : delf ft xs Just n -> delf (addToFM ft x (n-1)) xs delf _ [] = [] Should be O(|a|+|b|log|b|), I think. -kzm -- If I haven't seen further, it is by standing in the footprints of giants