On Apr 29, 2010, at 2:25 PM, Mark S. Miller wrote:
On Thu, Apr 29, 2010 at 12:08 PM, Mike Samuel <[email protected]>
wrote:
Yeah, I'm on the other side. I think that all new productions that
introduce a new keyword should be restricted. We have enough
semicolon insertion problems already!
:)
+1. I think all new productions should be restricted whenever the
lack of restriction creates either an actual semi-insertion problem,
or a visual confusion about whether there may be such a problem.
Really, methinks you guys protest too much. In particular Mike's "all
new productions that introduce a new keyword should be restricted" is
simply wrong for "let".
It is not as if we should have made "if", "else", "for", "switch",
etc. require the next token ('(' for "if", who knows what for "else")
to be on the same line. There is no ASI hazard with any of these
control-structure introducing keywords.
We're really talking about only postfix ++/--, "throw E", "return E",
"break L", and "continue L" if memory serves.
The other Harmony keyword in mind beyond "let", already reserved in
ES5 strict, and one which might indeed require a restricted
production, is "yield". If "yield" is supported as in JS1.7+ (after
Python 2.5+), you can write code like this:
js> function g() {yield; yield}
js> for (let i in g()) print(i)
undefined
undefined
You do not have to write "yield undefined;". It's an edge case but a
win when you need it, and it makes yield like return when used in a
statement context (we share the recursive descent parsing code in
SpiderMonkey).
Whether the infix "!" is used for binding or for asynchronous
message sending, it needs to be a restricted production so that
<left-operand>
! <stuff>
is not confused with
<expression-statement>;
! <unary-operand>
Specifically, infix "!" needs to prohibit a newline to its left.
Indeed, although there's no strawman proposal for "!" yet.
To quote dherman: syntax, yay.
/be
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