Wow, I wish I had decided to stop giving free updates before IDL 8.4 instead of before IDL 9.0 — there is a lot of new material in Modern IDL 1.4! There are new sections about treating all IDL variables as objects and functional programming, as well as the many minor updates of new routines. If you have purchased Modern IDL by PDF in the past, but didn’t receive an email this morning with a link to your new version of Modern IDL, please let me know.
Note that I am still planning to continue the free updates until IDL 9.0. At that point, I will have to decide based on what’s new in IDL 9.0 how it will continue (but it won’t be a free update).