A simple data type for storing year-isoweek dates in a human readable integer
format, e.g.: the 52nd isoweek of 2012 is stored as 201252. Supports simple
arithmetic operations such as + and - as well formatting.
Usage
date_yw(y, w)
is_date_yw(x)
as_date_yw(x)
Value
date_yw returns an object of type date_yw
is_date_yw returns TRUE or FALSE depending on whether its
argument is of type date_yw or not.
as_date_yw attempts to coerce its argument to date_yw