JP Bernardy
Would this make sense? Would it be useful?
I'm not sure that I understand either :)
Yeah, my definitions weren't exactly clear. I'll try to elucidate:
Let me give an example...
type MyString = MyString String
instance Eq MyString where (MyString x) == (MyString y) = length x == length y
I'm sure you'll agree that this is not something anybody sane would do. (Actually, I did something remotely similar, and I've regretted it ever since; it gave me some nasty, hard-to-track down bugs. I always derive Eq since then.) Which is why I think Bag perhaps should, instead of relying on Eq (or actually Ord, I suppose), be provided with a separate parameter specifying how to compare items for equality for bagging purposes.
Bag.toString $ Bag.fromString $ [ms "x", ms "y"]
So instead of doing this, I would like to be able to do mkBag myComp [ms "x", ms "y"] where myComp x y = compare (length x) (length y) which would then bag all equal-length strings (possibly storing them in multisets using regular Eq).
That is why I choose to keep the "MultiSet" name.
Just to make that clear, I've no issue with the naming.
If Eq is defined as structural equality, MultiSet and Bag are equivalent.
And since Eq "should" define structural equality, I propose a different interface for Bags (if we need them at all, that is) Was that a bit clearer? -kzm -- If I haven't seen further, it is by standing in the footprints of giants