I try to make a gdl-object by scripting.
I try to use the CWALL_ command to make someting like the illustration.
Everythig is understandable until the last parameters, a1, b1 ...
I've read the manual, but I need an example that is more like my figure.
My wall is just a simple wall with an opening in it.
cWALL_ or bWALL_ or xWALL_, just exist for compatibility with autoscripted objects. Don't use them, it's awful to script.
You get the same result inserting an empty opening into a wall. If you want to save it as object,
3D Window > Parallel projection > Top view 270° > File Menu > Libraries and Objects > Save 3D Model as Object > Editable script.
If so, take care to build your wall on project origin (grey cross), this will facilitate future changes in scripts.
If you prefer to script from scratch, better to use cPRISM_, or any similar tool.