Parser Rules

Parsers consist of a set of parser rules in either a parser or a combined grammar. A Java application launches a parser by invoking the rule function, generated by ANTLR, associated with the desired start rule. The most basic rule is just a rule name followed by a single alternative terminated with a semicolon.

 /** Javadoc comment can precede rule */
 retstat ​:​ ​'return'​ expr ​';'​ ​;

Rules can also have alternatives separated by the | operator.

 stat​:​ retstat
 |​ ​'break'​ ​';'
 |​ ​'continue'​ ​';'

Alternatives are either a list of rule elements or empty. For example, here’s a rule with an empty alternative that makes the entire rule optional:

 :​ ​'extends'​ ID
 |​ ​// empty means other ...

Get The Definitive ANTLR 4 Reference, 2nd Edition now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.