REPL in a Projectional Editor

I am implementing a Read Eval Print Loop into my structure editor, hoping for faster and more interactive development. I already knew I could use the editor as an interface, but haven't thought out the details.

Somewhat analogous to implementing a REPL in a text editor, I end up with a file. But I need to acknowledge this file should be able to contain any kind of structures, and I need to describe which schema does those structures follow. Therefole the REPL file is consisting of blocks. Each block represents for an input prompt or a response. Whenever the REPL responds, it appends a new block into this file.

Since every block defines a schema, the single REPL file can be used to prompt for different read eval print loops. The user can switch from the editor's interpreter into system shell and backwards. Additional shells could be opened and interfaced with, and the file could still contain that all.

The REPL could be turned into a customized display by opening monitors that update individual blocks in the file. To avoid confusion monitors would become gray when inactivated.