Good memories of MSM-Workstation! Glad to see that you are still working with the InterSystems technologies.

I think the looping affects the core tests, not the expr ones. 

https://github.com/intersystems/tree-sitter-objectscript/issues/8

+1 for more info about building and using.

So far I have succeeded in getting the tree-sitter playground working for the expr grammar:

My attempts to do the same with the core and udl grammars only give a blank screen there, and DevTools shows an error.