Existential Operator / Null Propagation Operator

Brendan Eich brendan.eich at gmail.com
Tue May 24 18:37:52 UTC 2016

You need to be very careful hacking around in an ad-hoc parser. It's easy
to diverge from the formal (and verified) grammar by accident. Ambiguous
grammars with ad-hoc disambiguation rules codified only by your parser's
source code are bad business. Voice of experience here.


On Sat, May 21, 2016 at 3:57 PM Isiah Meadows <isiahmeadows at gmail.com>

> I'm aware it's specified as a cover grammar, which is the easiest way I'm
> aware of to do it in a traditional declarative grammar. If you're writing a
> parser, though, you'll probably be using a mixture of lookahead and
> speculative parsing, or something to that effect, in practice, since it's
> faster.
> On Thu, May 19, 2016, 16:38 Kevin Smith <zenparsing at gmail.com> wrote:
>> I will note that JavaScript does already require n-token lookahead worst
>>> case to disambiguate arrow functions from sequence expressions.
>> The syntax is actually specified in terms of cover grammars, not
>> arbitrary lookahead.
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