How to create a new date range type with included upper bound in Postgres?

Question

Postgres comes with a nice feature called Range Types that provides useful range functionality (overlaps, contains, etc).

I am looking to use the daterange type, however I think the type was implemented with an awkward choice: the upper bound of the daterange is excluded. That means that if I defined my value as 2014/01/01 - 2014/01/31, this is displayed as [2014/01/01, 2014/01/31) and the 31st of January is excluded from the range!

I think this was the wrong default choice here. I cannot think of any application or reference in real life that assumes that the end date of a date range is excluded. At least not to my experience.

I want to implement a range type for dates with both lower and upper bounds included, but I am hitting the Postgres documentation wall: References on how to create a new discrete range type are cryptic and lack any examples (taken from the documentation: Creating a canonical function is a bit tricky, since it must be defined before the range type can be declared).

Can someone provide some help on this? Or even directly the implementation itself; it should be 5-10 lines of code, but putting these 5-10 lines together is a serious research effort.

EDIT: Clarification: I am looking for information on how to create the proper type so that inserting [2014/01/01, 2014/01/31] results in a upper(daterange) = '2014/01/31'. With the existing daterange type this value is "converted" to a [2014/01/01, 2014/02/01) and gives a upper(daterange) = '2014/02/01'

Answer 1

Notice the third constructor parameter:

select daterange('2014/01/01', '2014/01/31', '[]');
        daterange        
-------------------------
 [2014-01-01,2014-02-01)

Or a direct cast with the upper bound included:

select '[2014/01/01, 2014/01/31]'::daterange;
        daterange        
-------------------------
 [2014-01-01,2014-02-01)

Edit

Not a new type (wrong approach IMHO) but a proper function:

create function inclusive_upper_daterange(dtr daterange)
returns date as $$

    select upper(dtr) - 1;

$$ language sql immutable;

select inclusive_upper_daterange('[2014/01/01, 2014/01/31]'::daterange);
 inclusive_upper_daterange 
---------------------------
 2014-01-31