Today I made quite some progress, the addition of menus worked as intended. I had to extend some interfaces and change some internals of my UI-toolkit, but it wasn't very complex, just a lot of small changes. Then I added all the necessary parts to create a new operator, so now I can add new types and even use them. I also added a new operator class which will represent the result of the shader, I still have to add a bit to one function to make it impossible to delete it.
While playing a bit with the new functions I found and fixed some smaller problems. The biggest was, that the properties dialog didn't update when the selection changed. I have fixed that as well. So next is the addition of the channels to connect the operators. Then most of the boring stuff should be done and I can start with something more interesting, evaluating the operator graph and adding new operators.