> How about Bag, a set container? Alternately what we really want is
> just a Hash where the type of the value is defined as 1, so it need
> not be stored at all. Then most of the syntax for it just falls out
> of Hash syntax, unless you like writing $x ∈ $bag instead of $bag{$x}.
> Presumably we could make both work.
Please don't use bag as that is usually mathematically defined to be a
multi-set that can contain multiple copies of any given element. In
perl that would be a hash of Ints.
I'm not sure that immutable make any sense as a concept separate from
constant. A truly immutable object can't even be initialized, it has to
be born ex-nilo already with a value.
I think that only values (like 1, "ABC" and a set constant like
(1|2|5|9)) are immutable. So, we should just stick with variable and
constant (assigned once doesn't change afterwards) containers and not
use the term immutable at all.
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