[emmelaich]

I have a semi-made desk calculator with prefix notation.

You can make it an alias of * , / etc, so ...

   $ * 4 6
   24
   $

It would keep it's own stack, but let a persistent process do the actual maths.

The persistent process could almost any repl of python, ruby etc.

Or use a 'real' calculator like Pike's ivy; https://aplwiki.com/wiki/Ivy

[emmelaich]

Unfortunately, ( is not a valid alias name, so lispy things are difficult.

[ is a valid function name tho so fun could be had there.

[emmelaich]

Also = is a valid function name.

So you could use = to start the calc, and use infix or postfix notation.