ambiguous syntaxes

[royling]

When mixing ? and ... tokens, I guess only a set of syntaxes are valid imaging how the parser is going to work. Would you mind confirming the validity of the following syntaxes?

const f = (...x) => x

const g = f(?, 0, ..., ?) // valid?
const h = f(..., ?, 0, ...) // invalid? seems ambiguous

[rbuckton]

Originally, I intended the above to be approximately the same as this:

const g = (a, b, ...c) => f(a, 0, ...c, b);
const h = (a, ...b) => f(...b, a, 0, ...b);

However, following discussions at the September TC39 meeting, I think the following restriction makes sense:

• Neither ?, nor ... may follow ... in an argument list.

That would make both g and h above an error, though we could loosen this restriction slightly if we implement #5.

[rbuckton]

Closing as ... is currently disallowed as of the latest draft of this proposal.