At 7:28 PM -0700 9/25/06, Ashley Winters wrote:
On 9/25/06, Miroslav Silovic <[EMAIL PROTECTED]> wrote:
TSa wrote:
> role Set[::T = Item] does Collection[T] where {
> all(.members) =:= one(.members);
> };
> Nice usage of junctions!
But buggy - one means *exactly* one. So for an array of more than 1
element, all(@array) never equals one(@array) - if they're all the same,
it's more than 1, otherwise it's 0.
Yeah, that would've been cool. Are we left with asserting
C<all(.members »=:=« one(.members))>? That'd be pretty close to the
original elegance.
Ashley Winters
Unless I'm mistaken, you may be going about this the wrong way.
Within a system that already has an underlying
set-like type, the Junction in this case, a test
for uniqueness is (pardon any spelling):
all(@items).elements.size === @items.size
The all() will strip any duplicates, so if the
number of elements in all(@items) is the same as
@items, then @items has no duplicates.
Similarly, if @items is a list of Pair (such as
when you're implementing a Mapping), and you want
to assert that their keys are all distinct, then
this variation (pardon any spelling) would do it:
all(@items.map:{ .key }).elements.size === @items.size
Incidentally, a unique-key constraint on an RM
relation or table is like the latter as well, but
substitute "key" for the name(s) of the attribute
or column.
On the other hand, if you're using the above Set
to implement the Junction in the first place, we
can't use all/any/one/none etc in the definition.
-- Darren Duncan
