You can! At least with GitLab. Our pipelines are written in Python, and generate YAML that kick off child-pipelines. It's fairly trivial and works really well. Having for-loops and building an object based on functions making things so much easier.
You start to wonder thy you have to compile to 'yaml', instead of just having gitlab just give you a normale interface, in the form of a library. And then we've come full-circle.
