How to handle self-describing datatypes, e.g. ISO 8211
Hi, 

after unsuccessfully trying to write a ksy description for iso8211 files a few years ago, I started to try it again. I was successful in writing the general file pattern, but there is still some way to go.

How do these files look like? There is one DDR (data descriptive record) as first entry and n DRs (data records).

The entries in the DDR describe how to handle the data stored in the following DRs. These entries consist of mappings of tags like `SG2D` to descriptions like `2-D coordinate field\u001F*YCOO!XCOO\u001F(2b24)`. In this example the tag `SG2D` describes a coordinate with y and x values, which are both of the type `b24` (actually it is a bit more complex than that but should suffice for this description).

An entry in the DR contains a reference to a tag defined in DDR as well as data for that tag. To interpret the data, I theoretically have to find the tag in the DDR, interpret the type descriptions there and parse the data in the DR according to that description.

The first problem I have is how to search the array of tags in DDR for the current tag I have encountered in the DR entry. The next problem then would be how to interpret the type description taken out of the DDR and applying it to the data in the DR. Feels like some kind of dynamic typing.

Is such thing possible with ksy?