So far, MPS has only been able to project nodes at the location where they resided physically on the model. So, while the rendering of nodes could be designed arbitrarily, the structure of the projection itself always had to conform to the structure of the underlying AST. In other words, real views were not supported.

Enter querylist. A querylist is a list whose contents are the result of an arbitrary query over the model. The elements in the list can be editable, there are callbacks for what should happen when things are added or deleted, and it is even possible to define wrapper editors for the result elements or override the result element's editor completely.

We are using this currently in two places. First, we use it to show the signature of inherited operation-like constructs. In this case, the queried elements are rendered in grey, and they are readonly. The following picture shows this.

The second location where we currently make use of this feature is in assessments. So instead of just showing pointers to the result elements in the assessment result, we can now show the actual element inline. If the assessment is used to detect errors, then that error can be fixed directly in the assessment instead of navigating to the respective program location.

The querylist is not yet in MPS, but it is available on the mbeddr.platform.