New private names proposal

[David Herman]

> I think there are some interesting ideas to explore in both D. Flanagan's proposal and D. Herman's variations upon it.  However, they both seem to be ignoring the second primary use case that I identified: conflict-free extensions of build-in or third party objects.  While naming conventions or a sigil seems to be satisfactory to many as a way to implement "weak encapsulation".  I don't think it works for the extension case.

I guess the intended spirit of my admittedly not-fully-specified idea last night was that, other than the required '#' sigil, there's no major difference from the private names strawman on the wiki. In particular, you could still reify a private name in an expression context to get a value.

Let's just say, for the sake of concreteness, that the syntax would be:

    PrimaryExpression ::= ... | '#' Identifier

So you could do, for example:

    function gensym() {
        private #x;
        return #x;
    }

The exact lexical syntax isn't so much the point as just trying to avoid the ambiguity between public and private identifiers when used after dot or before colon by using a distinct lexical syntax for private identifiers. This way you don't have to know what's in scope to know *whether* an identifier is private.

Dave