Well, I've just waded through this discussion.
This all feels to me like a special case of "wanting a constant for
bytecode". What is we had a "freeze" operator, eg:
|foo|
which would produce a frozen version of foo. I'm liking the vertical
bars myself, I think because it feels vaguely slightly analogous to
"absolute value". So (assuming we can squeeze it into the expression
syntax):
|{1,2,3}|
always makes a direct frozen set on the same basis that:
x in {1,2,3}
directly makes a frozenset by expression inspection. Then
Paired with a __freeze__ dunder method, this applies to any type, not
just sets. (Where appropriate of course.)
So:
|{1,2,3}| frozen set
|[1,2,3]| tuple!
|any-iterable| tuple!
|{1:2, 3:4}| frozen dict
Ths saves us (a) inventing a special syntax for frozen sets and (b)
gateways to freezing many things, starting with the obvious above, via
the __freeze__ dunder method.
This feels more general and less bikeshedable.
My main question is: is the syntax unambiguous?
Cheers,
Cameron Simpson