On Fri, Jul 19, 2013 at 5:43 PM, Tab Atkins Jr. <[email protected]>wrote:
> On Fri, Jul 19, 2013 at 2:22 PM, Rick Waldron <[email protected]> > wrote: > > On Fri, Jul 19, 2013 at 3:21 PM, Tab Atkins Jr. <[email protected]> > > wrote: > >> On Fri, Jul 19, 2013 at 1:21 PM, Rick Waldron <[email protected]> > >> wrote: > >> > While this is all true, the simple answer is: > >> > > >> > var a = 1, b = 2, c = 3; > >> > a < b < c; // true > >> > > >> > is already valid JavaScript and can't be co-opted to express new > runtime > >> > evaluation semantics. > >> > >> Well, that's a bad example, because it's true with chained operators > >> too. Let c = 1.5, though, and you get different behavior. > > > > It doesn't matter if you think my example is a "bad example", it's a > valid > > expression per the language's existing grammar. > > It certainly does, because we don't expose the parsing directly. If > we change the interpretation of a piece of code, but it outputs the > same or compatible values, we're fine. It's only when the observable > results change incompatibly that we have to worry. In your example, > you get a "true" regardless of the interpretation, which means you're > not demonstrating a problem with changing the interpretation. > You have completely missed my point, please refer to the grammar specification that has existed since the first edition, published in 1997: MultiplicativeExpression : UnaryExpression MultiplicativeExpression * UnaryExpression MultiplicativeExpression / UnaryExpression MultiplicativeExpression % UnaryExpression AdditiveExpression : MultiplicativeExpression AdditiveExpression + MultiplicativeExpression AdditiveExpression - MultiplicativeExpression ShiftExpression : AdditiveExpression ShiftExpression << AdditiveExpression ShiftExpression >> AdditiveExpression ShiftExpression >>> AdditiveExpression RelationalExpression : ShiftExpression RelationalExpression < ShiftExpression RelationalExpression > ShiftExpression RelationalExpression <= ShiftExpression RelationalExpression >= ShiftExpression RelationalExpression instanceof ShiftExpression RelationalExpression in ShiftExpression EqualityExpression : RelationalExpression EqualityExpression == RelationalExpression EqualityExpression != RelationalExpression EqualityExpression === RelationalExpression (ES3+) EqualityExpression !== RelationalExpression (ES3+) Unambiguously and in no uncertain terms, the following is a completely valid expression (ie. will not throw a SyntaxError exception): 100 % 1 < 1e1 > 0xff - 5 + (+5) < 10 > 1.5 - 1..toString() === (function() {}()) !== parseInt(1, 10) * 1 | 0 >>> 1; // 1 It doesn't matter if the parsing isn't exposed, or broken in the first place, or a bad example, or not what you want, there is a formally defined grammar in a published standard. Hopefully I've cleared up any remaining questions or previously unclear points. Rick
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