When I started working commercially, my assembly language microcontroller programs ended up with read-eval-print loops and in some cases even a crude function-definition capability (more like shell scripting than true language extension) with an eval+apply function that checked for user-defined command scripts before going into its primitive list.

Why do I think FORTH immediately? Ah - we talked about that already :-)

(Some say that Forth is to assembly what Perl is to C)

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}