the default behavior of !include changed with preprocessorV2 to that of #include as in the C/C++ preprocessor. There, it is common practice to use include guards to prevent multiple inclusion of the same file. Multiple inclusions can also be harmful in PlantUML because they can easily lead to (infinite) cyclic inclusion.
Therefore I'm trying to replicate include guards with PlantUML preprocessorV2, see the example (render _view_seq.puml): https://github.com/zimtkeks/zimtkeks.github.io/tree/plantuml-include-guards/static/2019-03-08-plantuml-diagrams-without-redundancy (as ZIP)
The details are in _common_seq.iuml:10. I'm trying to check whether a variable has been already defined, whose name is composed of function arguments. If not, I define it. PlantUML gives me no useful error message. I'm not sure if it is at all possible to define a variable like this. But since the C/C++ preprocessor can do that, preprocessorV2 should be able to that as well (IMHO :-)
So, how can we get that to work?