What I would like to have (and looks quite similar to what you are describing) is some APL interpreter (or J or K...) with an RPN input method. The idea comes f

What I would like to have (and looks quite similar to what you are describing) is some APL interpreter (or J or K...) with an RPN input method. The idea comes from HP calculators, where you use RPN to "build" algebraic expressions. I have many ideas for such a system, but it will require much experimentation to get it right and, at this moment, is just vaporware.