Yeah the language here has a notion of the "last good state" so it can keep running. In the demo I'm not hitting "save" - the moment there's a good state, it becomes the "current version" - but there's no reason it needs to be that way.

I made the decision that state management is manual - the "once" keyword. Any expression/block not using "once" is re-evaluated any time there's a change to the code. If it's using it, it only re-evaluates if you change the (depth 0) code of that once wrapped expression.

In my case, only part of the program is recompiled and re-evaluated. The rest is located in a "committed" frozen area. Users can try new changes and throw them freely. The editor performs an evaluation/rollback on every keystroke, ensuring no accumulated or unintended changes to the stated were made during editing. When the user is satisfied and hit run, a long-term snapshot is created and the source code snippet is moving to the frozen area. Thats critical because the edit also rollback the file positions and streams.