Four types of RPN

[hansklav]

(09-02-2014 05:44 PM)Joe Horn Wrote:  Thanks for your excellent analysis of the differences!

However, I disagree that Greek letters are meaningful names. If something is "meaningful," then it's intrinsically full of meaning. It means that the listener can tell, just by hearing the name, what it's the name of. "Algebraic Entry mode" means something. "Textbook Display mode" means something. "Gamma" means nothing to anybody, until after it's explained, which proves that it's not intrinsically meaningful.

Even names that at first sight seem meaningful often need some explaining. This also applies to your examples. Only after having read the explanation is it relatively easy to remember what is meant by "Algebraic Entry mode" and "Textbook Entry mode". "Algebraic Entry mode" per se could just as easy be a good name for what now is called "Textbook Entry mode".

Greek letters per se are not meaningful, but they can be loaded with meaning. Everyone who has read more than one page about gorillas knows what is meant by an "alpha male". Mutatis mutandis the same goes for alpha, beta and gamma radiation.

(09-02-2014 05:44 PM)Joe Horn Wrote:  With all that in mind, I suggest these names:

Classical n-level RPN
Entry line n-level RPN
Infinite stack RPN

That's 11 possible names (n=4, 5, 8, 64, or 128),

I suggest "Entry line" instead of "Entry" because they ALL are forms of entry, so "entry" by itself is not specific enough. But only the "entry line" models use an entry line. We used to call that a "Command line" (remember the CLI on the Amiga?), but I guess it's called an "entry line" now. The Prime manual and built-in help system call it an "edit line".

I agree with you and Aristotle that it all starts with a good descriptive classification.
And that classification should include both HP and non-HP calculators, and also calculator programs (for computers, smartphones, tablets, etc.). There are many more RPN (of all types) calculator programs available (especially for smartphones) than there are RPN calculator models in hardware.

"Classical RPN" and "Entry line RPN" as classification for the two types of behaviour of the bottom of the stack is perfect to me. They're relatively well known to the community and both names have the same number of syllables. B.t.w.: in the Prime manual the command line is called "Entry line" and not "Edit line".

Imho your descriptive classification for the top of the stack is not entirely accurate, and misses the important point of presence or absense of "top copy on pop".

It is not accurate because an "infinite" stack can be combined both with Entry line RPN (e.g. the pre-Prime HP graphing RPN calculators) and with Classical RPN (the Mac OS X Calculator application). And the presence or absense of "top copy on pop" doesn't follow automatically from your classification. Some Entry line n-level RPN calculators have it (e.g. the HP 20b & 30b) and some don't (e.g. the HP Prime).

The word "infinite" denotes a specific mathematical concept (∞) and should better not be used for a stack that is only bounded by available memory. HP uses the word "unlimited" in this context, the computer science term is "unbounded". I would prefer one of those.

My proposal for a descriptive classification would be:
Each description of an RPN type includes three things:
- description of the bottom of the stack (Classical or Entry line RPN)
- presence or absence of "top copy on pop" (top-copy or top-neutral RPN)
- description of the hight of the stack (bounded n-level stack or unbounded stack)

At the moment in real life there exist only four types of RPN:
- Classical top-copy 4, 5 or 8-level stack RPN
- Classical top-neutral unbounded stack RPN
- Entry line top-copy 4-level stack RPN
- Entry line top-neutral 128-level or unbounded stack RPN

If we reshuffle this list so that all members of our community can easily remember it we get:
- Classical top-copy 4, 5 or 8-level stack RPN (the "classics", a.k.a. alpha type)
- Entry line top-neutral 128-level or unbounded stack RPN (the "graphics", a.k.a. beta type)
- Entry line top-copy 4-level stack RPN (the "??", a.k.a. gamma type)
- Classical top-neutral unbounded stack RPN (the "???", a.k.a. delta type)

Hans