Hi, Am Donnerstag, den 05.03.2015, 17:59 -0500 schrieb David Feuer:
1. A way to take the intersection of a list of sets. This shouldn't really be a big deal, and it already exists for unions, but the intersection version should probably sort the sets by size before folding, or otherwise try to do something smart.
+1
2. A way to insert an element if an == one is not already present (insert replaces an existing one with a new one). Currently, as far as I can tell, this can only be done using either
if e `member` s then s else insert e s which potentially descends the tree twice for no reason
or
s `union` singleton e
which is documented as being O(|s|+1), although I wouldn't be shocked if the documentation were too pessimistic in this case.
I’m doubtful about that one. This is only needed if == is not „the right equality“, in which case a Set might be the wrong data type. Do we want to advocate that style? Also, it will make everyone wonder „do I need insert or theOtherInsert“, making the API a bit less concise and quick to grasp. Since "s `union` singleton e" does the right thing with almost the right performance, maybe that’s sufficient?
3. A way to delete an element and simultaneously find out whether it was in the set.
+1, possibly with the type a -> Set a -> Maybe (a, Set a) to get the remaining set as well. Greetings, Joachim -- Joachim “nomeata” Breitner mail@joachim-breitner.de • http://www.joachim-breitner.de/ Jabber: nomeata@joachim-breitner.de • GPG-Key: 0xF0FBF51F Debian Developer: nomeata@debian.org