Confused about expressions in Prime RPN stack

[Orome]

(04-26-2020 07:50 PM)rprosperi Wrote:  

(04-26-2020 06:27 PM)Orome Wrote:  On a Prime I can't get it back. So maybe one way of thinking abut the question is: why are the Prime semantics for picking different?

The Prime supports RPN, but nothing of RPL, except some extensions for types. So it behaves more like a 35S than a 48S.

Yes, but the 35s doesn't let me create a formatted expression, which is how this issue arises.

The question is why I can use the Prime's "template" to create an algebraic — actually I guess "textbook" — expression which I can put on the stack and evaluate (and even perform operations on in the same way as I can on an RPL model; e.g. I can follow the creation of the expression with [2][+] and get the expected textbook formatted expression as a result); but if I pick it and press [ENTER], I get something that's considered invalid and can do nothing further with.