There is an alternative: a quick start GUI mini-IDE which allows you to type in and edit the code and press a button to run it. Such tools are mandatory on Windows anyhow: Ocaml and Python both have this for example. Most Unix editors like Vim or Emacs could be programmed to do this fairly easily I guess. I even wrote such a tool once using Tcl/Tk.

I agree this is not the same as a REPL with line by line interactive execution/editing with an environment that saves well defined symbols. Ultimately this would be tough to see through because Felix binds functions statically and lookup is setwise (like function scope in C) not linear, so recursive definitions cannot be introduced one at a time.