Irrlicht Engine

I'm currently working on exposing the GUI classes and methods to Angelscript. IGUIEnvironment appears to be almost entirely composed of pure virtual functions. Angelscript does not allow me to register virtual functions in this manner, and IGUIElement, another class I am registering depends on IGUIEnvironment as a parameter. So, my question is, where are the functions for IGUIEnvironment implemented and why are they pure virtual methods?

Look at the source folder.

you will find a CGUIEnvironment.cpp and its header file.
Using an abstract class allows user to create their own GUI environment easily.

I am surprised Angelscript doesn't allow you to bind such methods. With luabind you can.