Subsumption in partially ordered sets
GK at ninebynine.org
Tue Nov 18 10:50:30 EST 2003
At 09:14 18/11/03 +1300, Tom Pledger wrote:
>Graham Klyne writes:
> | Below is some code I have written, which works, but I'm not sure
> | that it's especially efficient or elegant. Are there any published
> | Haskell libraries that contain something like this?
>Partially ordered sets are in cahoots with lattices, so you may be
>interested in http://www.cse.ogi.edu/~mpj/pubs/lattices.html .
That might be interesting... is full paper available online? (I don't have
easy access to a serious technical library.)
>And here's some off-the-cuff feedback...
>How about using Maybe Ordering, instead of a new data type?
>(As in http://email@example.com/msg05635.html)
Duh. That sounds like an excellent idea - I knew there was a reason for
posing dumb questions like these!
>Instead of hard-wiring Maybe into the element type in dropSubsumed,
>how about passing in a partial comparison function?
> dropSubsumedBy :: (a -> a -> Maybe Ordering) -> [a] -> [a]
Yes, I agree that would be neater.
(Though I was aware that this code was too specialized in many ways. I
have noticed that it's often easier (for me) to code for a specific
situation and then generalize the resulting code, than to go immediately
for the general case. Haskell seems to be particularly well suited to
factoring out the type-specific bits in this way, I think because it's
often easy to parameterize any piece of code as a higher order function.)
Thanks for your insights!
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