Antlr3 grammar file

For example, the following simple rule has a nondeterministic subrule, which arises from a language ambiguity that you could attach an ELSE clause to the most recent IF or to an outer IF because the construct can nest. Because the language is ambiguous, the context-free grammar must be ambiguous and the resulting parser nondeterministic in theory. However, being the practical language folks that we are, we all know you can trivially solve this problem by having ANTLR resolve conflicts by consuming input as soon as possible; I have yet to see a case where this was the wrong thing to do, by the way.

This option, when set to false, merely informs ANTLR that it has made the correct assumption and can shut off an ambiguity related to this subrule and an empty alternative or exit path. Here is a version of the rule that does not yield a warning message:.

One important note: This option does not affect non-empty alternatives. For example, you will still get a warning for the following subrule between alts 1 and 3 upon lookahead A :. Further, this option is insensitive to lookahead. Only completely empty alternatives count as candidate alternatives for hushing warnings. See the parser speed section above. The case of the input stream is maintained when stored in the token objects.

The grammar analysis and, hence, the lookhaead sets are aware of the whitespace references. This is a lexer rule option. In Java, this amounts to a comma-separated list of interfaces that your lexer, parser, or tree walker must implement. The default is true. Use this very carefully--you may change the subrule and miss an ambiguity because of the option.

ANTLR-generated parsers resolve ambiguous decisions by consuming input as soon as possible or by choosing the alternative listed first. False implies you want subrule loop,.. Specify the type of all user-defined labels, overrides default of AST. Both the lexer and the parser have an interactive option, which defaults to "false".

Case is ignored when comparing against character and string literals in the lexer. Specify a lexer rule to use as whitespace between lexical rule atomic elements chars, strings, and rule references.

An easy way to specify a string to use in place of the token name during error processing. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Podcast Helping communities build their own LTE networks. Podcast Making Agile work for data science. Featured on Meta. New post summary designs on greatest hits now, everywhere else eventually. Linked 7. Related Hot Network Questions. Question feed.

Stack Overflow works best with JavaScript enabled. A rule definition inside an antlr grammar corresponds to a method definition in the generated java file. As you can see , here again we can do everything with a rule , that can be done with a function. We can specify arguments for the rule ,as shown above int a , even a return value and the exceptions thrown by the rule. The options section allows us to specify some rule specific options. We can specify custom exception handlers in the exception section.

You get the parse tree as a result of interpreting a grammar. Imagine passing some input to a rule in your grammar and instantly seeing how the rule matches the input. We designed the debugger to work like TiVo: you can pause a running parser and then rewind it! Once a parse has completed, ANTLRWorks has a complete trace and allows the user to walk back and forth over the input stream like a video camera.