A simple data type for storing year-month dates in a human readable integer
format, e.g.: December 2012 is stored as 201212. Supports simple
arithmetic operations such as + and - as well formatting.
Usage
date_ym(y, m)
is_date_ym(x)
as_date_ym(x)
Value
date_ym returns an object of type date_ym
is_date_ym returns TRUE or FALSE depending on whether its
argument is of type date_ym or not.
as_date_ym attempts to coerce its argument to date_ym