The Definitive ANTLR 4 Reference, 2nd Edition

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 ...