stack lift and change sign

[Paul Dale]

(08-29-2014 12:55 PM)walter b Wrote:  Hmmmh, what would be the benefit over classic RPN?

Quite a bit. It is more consistent to not have stack lift.

Type in a value and press ENTER. The value goes into X, the stack lifts one position. This is the same behaviour as e.g. PI. You don't use two stack levels for entering one number, you don't risk things like 3 ENTER 4 ENTER + (which was asked about recently from memory).

Clx drops the stack one level, rather than putting zero into X and disabling lift. It needs a rename but there is no odd behaviour anymore.

Sigma+ and Sigma- play stack games too. Consistent is for them to consume two levels and to rely on an UNDO command to fix a mistake.

% is another one. Yes, leaving the value in Y is handy if followed by + or - but confusing and inconsistent.


Basically, you are getting rid of quite an oddity (stack lift) and doing everything in a consistent and sensible manner. The oddity was due to early device not having enough memory. I'm sure HP wouldn't have had stack lift if the HP 35 had had a couple of extra registers in the CPU.


How many times have we had questions for new members that came down to stack lift issues? I can remember several, I also remember getting confused after coming back to RPN from RPL by this exact issue.


- Pauli