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]
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