presto-parser/src/main/java/io/prestosql/sql/parser/AstBuilder.java/AstBuilder/visitArithmeticUnary
class AstBuilder:    @Override
    public Node visitArithmeticUnary(SqlBaseParser.ArithmeticUnaryContext context)
    {
        Expression child = (Expression) visit(context.valueExpression());

        switch (context.operator.getType()) {
            case SqlBaseLexer.MINUS:
                return ArithmeticUnaryExpression.negative(getLocation(context), child);
            case SqlBaseLexer.PLUS:
                return ArithmeticUnaryExpression.positive(getLocation(context), child);
            default:
                throw new UnsupportedOperationException("Unsupported sign: " + context.operator.getText());
        }
    }