On Fri, 17 Mar 2000, David Ascher wrote:
> > I think the semantics would be pretty understandable and simple to
> > explain, which is the main thing.
> >
> > Any thoughts?
>
> Would
>
> (a,b) in Set
>
> return true of (a,b) was a subset of Set, or if (a,b) was an element of Set?
This would return true if (a, b) was an element of the set --
exactly the same semantics as we currently have for lists.
Ideally it would also be kind of nice to use < > <= >= as
subset/superset operators, but that requires revising the
way we do comparisons, and you know, it might not really be
used all that often anyway.
-, |, and & could operate on lists sensibly when we use
them as sets -- just define a few simple rules for ordering
and you should be fine. e.g.
c = a - b is equivalent to
c = a
for item in b: c.drop(item)
c = a | b is equivalent to
c = a
for item in b: c.take(item)
c = a & b is equivalent to
c = []
for item in a:
if item in b: c.take(item)
where
c.take(item) is equivalent to
if item not in c: c.append(item)
c.drop(item) is equivalent to
while item in c: c.remove(item)
The above is all just semantics, of course, to make the point
that the semantics can be simple. The implementation could do
different things that are much faster when there's a hash table
helping out.
-- ?!ng
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