Something that has been much sought after over the years, but most of the programming snippets come from the forum or other Turbocad users. I have scoured the internet a few times, and not one book on programming for Turbocad, well there is one relating to enable basic in Turbocad V4. If you look for Autocad programming books, you will find masses of books.
If Turbocad is to move ahead and compete with Autocad, and it certainly has the tools, it needs to start producing more about the programming of it's excellent toolset.
Also a good project for a technical or Programming Author.