Can we have RPN back?

[John R. Graham]

(03-27-2014 04:08 PM)orcinus Wrote:  ...Edit: On top of that, RPL is a natural extension of RPN. No one's forcing you to use >4 stack levels.

Arguably, this is true. I like the extensions. However, RPL (Entry RPN) isn't a fully compatible extension of legacy RPN. That's what the OP was asking for: a compatible legacy RPN mode for Prime. I don't want it, but I understand the request.

The two major differences are (I believe):

• Behavior of stack lift. Starting with an empty stack, "2 [Enter] x" results in 4 on legacy RPN calculators and an error on RPL calculators (and the Prime).
• Auto-copy of T. As operators consume the contents of the stack, on legacy RPN calculators, the contents of T is duplicated into Z so that the stack never truly empties. (In fact, the stack always contains 4 numbers.) On RPL machines, the stack can actually empty, resulting in operation not being able to complete for lack of arguments.
  

Of the two, I think the first is the most important behavioral attribute to the legacy RPN crowd. I've taken advantage of the behavior on the 35/67/97/41 myself, but I think the more recent behavior is more internally consistent, even though (gasp) it takes an additional keypress for some operations.

- John