presto-parser/src/main/java/io/prestosql/sql/parser/AstBuilder.java/AstBuilder/visitInterval
class AstBuilder:    @Override
    public Node visitInterval(SqlBaseParser.IntervalContext context)
    {
        return new IntervalLiteral(
                getLocation(context),
                ((StringLiteral) visit(context.string())).getValue(),
                Optional.ofNullable(context.sign)
                        .map(AstBuilder::getIntervalSign)
                        .orElse(IntervalLiteral.Sign.POSITIVE),
                getIntervalFieldType((Token) context.from.getChild(0).getPayload()),
                Optional.ofNullable(context.to)
                        .map((x) -> x.getChild(0).getPayload())
                        .map(Token.class::cast)
                        .map(AstBuilder::getIntervalFieldType));
    }