Stijn De Saeger wrote:
Now, for unions I tried the following: to take the union of two BasicSets, just append them and contract the result. contracting meaning: merge overlapping intervals.
contract :: Range -> Range -> BasicSet contract (x1,y1) (x2,y2) | x2 <= y1 = if x2 >= x1 then [(x1, (max y1 y2))] else if y2 >= x1 then [(x2, (max y1 y2))] else [(x2,y2), (x1,y1)] | x1 <= y2 = if x1 >= x2 then [(x2, (max y1 y2))] else if y1 >= x2 then [(x1, (max y1 y2))] else [(x1,y1), (x2,y2)] | x1 <= x2 = [(x1,y1), (x2, y2)]
Now generalizing this from Ranges to BasicSets is where i got stuck. In my limited grasp of haskell and FP, this contractSet function below is just crying for the use of a fold operation, but i can't for the life of me see how to do it.
As the result is a BasicSet, the accumulator would need to be a
BasicSet and the operator would need to have type:
BasicSet -> Range -> BasicSet
This can presumably be implemented as a fold on contract, so
contractSet would essentially be a doubly-nested fold.
--
Glynn Clements