Four types of RPN

[Joe Horn]

(09-02-2014 09:38 PM)walter b Wrote:  

(09-02-2014 05:44 PM)Joe Horn Wrote:  Classical n-level RPN
Entry line n-level RPN
Infinite stack RPN

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

There are different entry-line RPN models AFAICS: those with top level repetition and those without. Cf. the HP-30b (EL 4-level with TLR) and the Prime (EL 128-level without TLR).

(Just brainstorming here...) Well, if we limit ourselves to existing implementations (a reasonable thing to do), then everything fits in exactly one of these six groups of RPN models, thus making them unambiguous:

Classical 4-level RPN (most models)
Classical 4&8-level RPN (WP 34s)
Entry-line 4-level RPN (20b, 30b, any others?)
5-level RPN (what model had 5 levels???)
128-level RPN (Prime)
Infinite stack RPN (RPL models)

There's no need to specify top-level replication, because that's not ambiguous within any of those groups. "Top-level-replicating 128-level RPN" is redundant, because all 128-level RPN's are non-top-replicating. (All one of them.) Similarly, we don't need to mention whether CLx disables stack lift or not, since all the models within each group handle that the same way. Ditto for all features shared within each group. No? (I might be forgetting some models...)

It's tempting to call 128-level RPN "Prime RPN" because only Prime has it... but that's only true at this time. Who knows; other models might have it later, and "Prime RPN" only names it, but doesn't describe it. So 128-level RPN is a better name. Ditto for Classical 4&8-level RPN.

Wasn't there a 3-level RPN in some ancient desktop models? And somebody recently mentioned a model that used Y as the accumulator (bizarre!). We'd need to extend the above table if we want to include those critters.