On Thu, 11 Jan 2007, Seth Gordon wrote:
I have a data type "Group", representing a group of geographic information that is all referring to the same location, and a function "mergeGroups" that tries to merge two groups:
mergeGroups :: Group -> Group -> Maybe Group
Then I have a function "mergeGroupToList" that tries to merge its first argument with every element of the second argument:
mergeGroupToList :: Group -> [Group] -> [Group] mergeGroupToList g [] = [g] mergeGroupToList g1 (g2:gs) = case (mergeGroups g1 g2) of Nothing -> g2 : (mergeGroupToList g1 gs) Just g3 -> mergeGroupToList g3 gs
Is mapAccumL also allowed? Untested but type-checked: mergeGroupToList g0 gs = let (mergedG, unmergedGs) = mapAccumL (\g1 g -> maybe (g1, Just g) (\g3 -> (g3, Nothing)) (mergeGroups g1 g)) g0 gs in catMaybes unmergedGs ++ [mergedG]