presto-parser/src/main/java/io/prestosql/sql/parser/AstBuilder.java/AstBuilder/getIntervalSign
class AstBuilder:    private static IntervalLiteral.Sign getIntervalSign(Token token)
    {
        switch (token.getType()) {
            case SqlBaseLexer.MINUS:
                return IntervalLiteral.Sign.NEGATIVE;
            case SqlBaseLexer.PLUS:
                return IntervalLiteral.Sign.POSITIVE;
        }

        throw new IllegalArgumentException("Unsupported sign: " + token.getText());
    }