Have a copy of “Programming the Be Operating System” available. Don’t know if it is relevant to Haiku. Just send me an email to email@example.com
First, the book is still a very useful programming guide for Haiku, there is on this website in the development section an URL that points to the differences between Haiku and BeOS programming. For user applications the changes are not that much.
Second, the book is also available as a PDF on this website, also in the development resources section.