Jon Lang wrote:
That saves a singlr character over Bag( ... ) and Set( ... ),
respectively (or three characters, if you find decent unicode bracket
choices).  It still wouldn't be a big enough deal to me to bother with

As well, my first impression upon seeing [! ... !] was to think
"you're negating everything inside?"  That said, I could get behind
doubled brackets:

    [[1, 2, 3]] # same as Bag(1, 2, 3)
    {{1, 2, 3}} # same as Set(1, 2, 3)

I prefer to have the mnemonic that {} means unordered and that [] means ordered, so please stick to [] meaning arrays or ordered collections, an {} meaning unordered collections, so set and bag syntax should be based around {} if either.

This said, I specifically think that a simple pair of curly braces is the best way to mark a Set.


  {1,2,3}  # a Set of those 3 elements

... and this is also how it is done in maths I believe (and in Muldis D).

In fact, I strongly support this assuming that all disambiguation eg with hashes can be specified.

  {a=>1,b=>2}  # a Hash of 2 pairs

  {:a<1>, :a<2>}  # we'll have to pick a meaning

  {}  # we'll have to pick a meaning (Muldis D makes it a Set; %:{} is its Hash)

  {;}  # an anonymous sub or something

  {a=>1}  # Hash

  {1}  # Set

  {1;}  # anonymous sub or something

But keep that simple an let nesting work normally, so:

  {{1}}  # a Set of 1 element that is a Set of 1 element

  {{a=>1}}  # a Set with 1 Hash element

  {[1]}  # a Set with 1 Array element

  [{1}]  # an Array with 1 Set element

In certain cases, we can always still fall back to this:

  Set()  # empty Set

  Hash()  # empty Hash

  Set(:a<1>)  # if that's what we wanted

As for bags, well I think that is where we could get fancier.

But *no* doubling up, as we don't want to interfere with nesting.

Instead, it is common in maths to associate a "+" with set syntax to refer to bags instead.

So, does Perl already ascribe a meaning to putting a + with various bracketing characters, such as this:

  +{1,2,2,5}  # a Bag of 4 elements with 2 duplicates

  +{}  # an empty Bag, unless that already means something

So would the above try to cast the collection as a number, or take the count of its elements, or can we use something like that?

But I would recommend something along those lines.

I suppose then if +{} works for bags we could alternately use -{} for sets but I don't really like it.

-- Darren Duncan

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