This answer is incorrect - the '.' will be the same token. See my earlier answer.
Jim > -----Original Message----- > From: antlr-interest-boun...@antlr.org [mailto:antlr-interest- > boun...@antlr.org] On Behalf Of Kirby Bohling > Sent: Monday, November 28, 2011 8:18 AM > To: Christian > Cc: antlr-interest@antlr.org > Subject: Re: [antlr-interest] Confused about backtracking > > On Mon, Nov 28, 2011 at 9:02 AM, Christian <chw...@gmx.de> wrote: > > Mh, I am with you. I also do not understand backtracking in this > > situation ;) > > > > Could anyone else explain it, please? > > Pretty sure you are having problems because you have '.' as an > inline/generated token in your rules. I've said it dozens of times on > this list, hopefully long time reader's don't think I'm irritating, but > if you aren't Dr. Parr, I'd highly recommend forcing generating all > tokens with Lexer rules, and never, ever generate them with inline > tokens. I'm pretty confident that your problem is that the '.' is > generating the token in the "sep" rule, which won't match the token > generated in the "expr" rule (and only one of them will ever be > generated). I really like the conciseness of the examples when the > inline lex rules are used, but every time I try them, it because a > problem for me. > > So, the first rule is, never use inline tokens. The second rule is > print the tokens out, and manually parse walk them through the parser. > Every time I get stuck, and am sure the ANTLR has a bug, I remember > these rules, and then realize that I did something silly. I don't have > an ANTLR toolchain handy so I can't try it, but I'm pretty sure that's > what is wrong. > > I believe one step forward is to add a lex rule: > > DOT: '.'; > > Then replace your inline '.' in sep and expr with that token. I'll be > that moves you forward (not sure it will solve it). > > Finally, remember, in ANTLR the lexer logically (even if it doesn't > actually) runs start to finish and generates all of the tokens. Then > the stream of tokens are handed the parsers. There is no backtracking > where the parser gives up, and the lexer tries other alternatives. > > Kirby > > > > > > Am 28.11.2011 15:18, schrieb franck102: > >> Christian wrote > >>> Hi, > >>> > >>> what is the error/exception message? > >>> > >>> Regards, > >>> Christian > >>> > >>> > >> MissingTokenException at the second '=', after parsing a=b.c as an > >> expression. The tail recursion on expr is causing it it seems, but > >> that's a real issue for me... here is a slightly modified version > >> with the recursion made explicit that has the same problem: > >> > >> program > >> : statement* EOF > >> ; > >> > >> statement > >> : ID '=' expr > >> | sep > >> ; > >> > >> expr : ID ( '.' expr )*; > >> > >> sep : ';' | '.'; > >> > >> -- > >> View this message in context: > >> http://antlr.1301665.n2.nabble.com/Confused-about-backtracking- > tp7033 > >> 712p7038881.html Sent from the ANTLR mailing list archive at > >> Nabble.com. > >> > >> List: http://www.antlr.org/mailman/listinfo/antlr-interest > >> Unsubscribe: > >> http://www.antlr.org/mailman/options/antlr-interest/your-email- > addres > >> s > >> > > > > > > List: http://www.antlr.org/mailman/listinfo/antlr-interest > > Unsubscribe: > > http://www.antlr.org/mailman/options/antlr-interest/your-email- > address > > > > List: http://www.antlr.org/mailman/listinfo/antlr-interest > Unsubscribe: http://www.antlr.org/mailman/options/antlr-interest/your- > email-address List: http://www.antlr.org/mailman/listinfo/antlr-interest Unsubscribe: http://www.antlr.org/mailman/options/antlr-interest/your-email-address -- You received this message because you are subscribed to the Google Groups "il-antlr-interest" group. To post to this group, send email to il-antlr-inter...@googlegroups.com. To unsubscribe from this group, send email to il-antlr-interest+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/il-antlr-interest?hl=en.
