[Haskell-cafe] Set of reals...?

Keith Wansbrough Keith.Wansbrough at cl.cam.ac.uk
Fri Oct 29 06:14:44 EDT 2004

[(Double,Double)] is not enough - you need to know if each end is open 
or closed.  Also note that you will have to use -infinity and +infinity 
(-inf and +inf) to model things like the complement of (1.0,2.0).

Which brings me to a question: is there a better way to write -inf and 
+inf in Haskell than "-1/0" and "1/0"?

Your data structure should be something like:

data Interval = Interval {
	left :: Double,
        leftopen :: Bool,
        right :: Double,
        rightopen :: Bool

data Set = Set [Interval]

If you want more efficiency, you probably want a bintree datastructure 
(search Google for "quadtree" and "octree", and make the obvious 
dimension shift).

--KW 8-)
Keith Wansbrough <kw217 at cl.cam.ac.uk>
University of Cambridge Computer Laboratory.

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