public virtual ParseTreePattern CompileParseTreePattern(string pattern, int patternRuleIndex){if (((ITokenStream)InputStream) != null){ITokenSource tokenSource = ((ITokenStream)InputStream).TokenSource;if (tokenSource is Lexer){Lexer lexer = (Lexer)tokenSource;return CompileParseTreePattern(pattern, patternRuleIndex, lexer);}}throw new NotSupportedException("Parser can't discover a lexer to use");}