Regarding (2), I was thinking about situations where sharing is an issue. Even if == is the right equality, you may want to settle on a single copy. That would also suggest a version of member that returns a Maybe instead of a Bool.
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/
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