[npsimons]

> An embedded Lisp that supports a true REPL would be a god-send.

I might be misunderstanding your requirements; "embedded" can mean so many things these days. But what do you think of ECL (https://ecl.common-lisp.dev/main.html)?

[HexDecOctBin]

I am thinking more like Lua where you can create thousands of lua_State, and run them all independently with none of them messing up the global state of the application. Something which is self-contained, portable, runs in a VM, doesn't use global state, whose execution can be controlled from the outside with hooks, etc.

I don't know if ECL is disciplined enough to actually constraint itself in all these ways to be a good embedded citizen.