I'm trying to write some new statements to create an internal C DSL. The tool of my choice is MPS and the base is the c-core of mbeddr. I found this  tutorial on the internet. Since it is a little old, I am not able to duplicate the exact structure of the setup itself.
What I want to do is to create a new language. The language must be extended by com.mbeddr.core. I found, how to extend the language and did so. I needed to extend every single language com.mbeddr.core.* by its own, everything else did not work (it does not even work properly now).
The I created a new statement in a structure module. There I extended the concept to a Statement (c.m.c.statements.structure is shown). Then, following the video tutorial, I wanted to add an expression as a child, this is where it fails.
I am not sure where I went wrong here. It is very difficult to set it up properly, since all tutorials/guides are outdated.
Thanks for your help,