code: Rule Literal() {
          return Sequence(
                  FirstOf(
                          FloatLiteral(),
                          IntegerLiteral(),
                          CharLiteral(),
                          StringLiteral(),
                          Sequence("true", TestNot(LetterOrDigit())),
                          Sequence("false", TestNot(LetterOrDigit())),
                          Sequence("null", TestNot(LetterOrDigit()))
                  ),
                  Spacing()
          );
      }
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