At 21:59 21/04/2009, Avid Trober wrote: >I'm parsing a 7-bit ASCII stream ... 2 questions > >Question 1: can't I just fall-thru wrt to lexer rules, where >lexer rules are specific-to-general, and avoid indeterminisms at >run-time? [...] >... // (AND IF NOTHING ABOVE MATCHES, AT LEAST WE'RE MATCHING >HERE ... ) > >CHAR : '\u0000'..'\u007F' // any 7-bit US-ASCII character > ;
You can specify a catch-all match like so: CHAR : .; If this is the last lexer rule, then it will behave as you're expecting. >Question 2: I'm at a loss how to match the notation in the spec >I'm writing a grammar for where binary digits are '0' or '1' and >digits are '0'..'9'. (ABNF-ish) It is prefered to make the >grammar rule names match that (whether lexer or parser, it >doesn't matter) Generally, it's best to have the lexer match as wide as possible (ie. have DIGIT, not BINARY_DIGIT) and sort it out in the parser, where you can use the context to give better error messages if you encounter something invalid. >Can I write a binary_digit parser rule that works with DIGIT >above somehow? Yep. Depending on the context, you may want to either use a lookahead-based entry predicate to avoid entering the rule if the DIGITs aren't binary-safe, or a exit predicate that raises an error if it turns out that the sequence wasn't valid binary. 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-interest@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 -~----------~----~----~----~------~----~------~--~---
