On Oct 17, 2008, at 7:36 PM, Eric Suen wrote: > Are you sure about that, because you using hand written top-down > parser, > Is it confirmed by a top-down parser generator like ANTLR?
I haven't used ANTLR or any other LL(*) parser generator, no. I found http://code.google.com/p/antlr-javascript/ and wondered if anyone on the list has evaluated it. > I think top-down parser has no issue to parse following code: > > function() { > }(); Agreed. > but this is not a valid statement because: > > ExpressionStatement ::= [lookahead ! {{, function}] Expression ; That's a good example. See https://bugzilla.mozilla.org/show_bug.cgi?id=376052 if you are interested in why people want to evaluate such a statement. > This kind question I asked long time ago, but no one answed, > > https://mail.mozilla.org/pipermail/es-discuss/2008-July/006640.html Sorry, Jeff may have missed your question. I don't understand it myself (no one ever proposed any syntax of the form x = function () return y). > and now seems write a bottom up JS parser is mission impossible. Why do you say that? Maciej already cited the Bison grammar that WebKit's JS engine uses. Waldemar has an out of date but ambitious bottom-up grammar checker. The question before us is what to standardize and how to check it. An extension like let expressions is not a foregone conclusion, likewise expression closures (which some folks in TC39 at the Oslo meeting favored). If we don't want ambiguities that create prove-a- negative hazards, we won't standardize these as-is. For example, we could require parenthesization of the AssignmentExpression body; or we could do something else, such as the braced lambda body that's been discussed here recently. If you mean bottom-up parsing of JS1.7 as implemented in SpiderMonkey is impossible, I still wouldn't go that far. C and C++ are not easy to parse bottom-up, but even ignoring lexer/parser feedback, it can be done with enough hacking, AFAIK. The C-like languages including JS do not inherit bottom-up grammar bones from bad old C. The C top-down grammar (dmr's original C compiler used recursive descent and operator precedence parsing) shows through pretty clearly. I agree we shouldn't make things worse. I don't think all hope is lost. /be _______________________________________________ Es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
