Heredoc in ANTLR 4 demo

Heredoc.g4

grammar Heredoc;

@lexer::members {
  public boolean heredocValid (String str) {
    String[] lines = str.split("\n");
    String first = lines[0], last = lines[lines.length - 1];
    return first.substring(2).equals(last);
  }
}

Identifier: [a-z]+;
WS: ' ' -> skip;
Heredoc:
  '<<' Identifier Newline
  (.+? Newline)?
  Identifier Newline {heredocValid(getText())}?;
Newline: '\n';

program: (Identifier | Heredoc | Newline)+ EOF;