What Is RPN? Why Did/Does HP Use RPN? Learning RPN (1999) • Hacker News Board

Re: What Is RPN? Why Did/Does HP Use RPN? Learning RPN (1999)

#41

Post by tome » Sat, Mar 06, 2021, 9:30 PM UTC

ajarmst wrote: post #26

jeffbee wrote: post #9

Earlier quoted context omitted.

Yeah, it feels like the whole "why" is that RPN reflects how the machine works, so it's easier to build it that way.

Well, it’s easier to build because it has a terse syntax that requires fewer symbols, doesn’t need precedence and associativity rules, and has no ambiguous instructions. It’s easier to use for the same reasons.

> has no ambiguous instructions

Really? What do you call an operator applied to an empty stack? A sequence of commands that leaves the stack non-empty? I don't see why that's any less ambiguous than mismatched parentheses.

Re: What Is RPN? Why Did/Does HP Use RPN? Learning RPN (1999)

#42

Post by kuon » Sat, Mar 06, 2021, 9:31 PM UTC

RPN is a lot like vim, the first time you are like DUH! I can't add 2 and 2. But if you take the learning curve, it becomes very efficient and you cannot move back.

Re: What Is RPN? Why Did/Does HP Use RPN? Learning RPN (1999)

#43

Post by spullara » Sat, Mar 06, 2021, 9:32 PM UTC

I did so much programming on the HP 28S and the HP 48Gx. Really an awesome mobile programming platform at the time.

Re: What Is RPN? Why Did/Does HP Use RPN? Learning RPN (1999)

#44

Post by tzs » Sat, Mar 06, 2021, 9:33 PM UTC

jjav wrote: post #32

disabled wrote: post #8

It took awhile to learn RPN in undergrad in electrical engineering. But, once you learn it, it is so much easier to solve problems and it is much more efficient. You never go back, and you are less likely to make errors entering in equations compared to your peers. This is important on timed exams. I prefer to always use RPN. MacOS has an RPN mode on their calculator, which one can activate by pressing command + R. O…

RPN is so nice and efficient, can't imagine using anything else. I like that the OSX calculator does RPN. But mostly I use my old 28S which is next to my keyboard always. Also have a 50g on the desk, but I prefer the 28S.

I get annoyed by the ways the OS X calculator deviates from HP RPN.

The main one is that the pi and e keys act as if they are invoking constant functions that return pi and e, respectively. On an HP calculator, the pi key enters pi.

That may sound like the same thing, but it is not. Consider this sequence:

  2 ln  pi x

On my HP 15C the result is to multiply the natural log of 2 and pi. Same thing with PCalc on my iPhone. With OS X calculator the result is either pi with an error beep if you started with an empty stack or pi times whatever was on the top of the stack if you started with a non-empty stack.

The "2 ln" part leaves ln(2) on the stack. On the HP and other sensible calculators the pi key pushes pi. On the MacOS calculator, it replaces the top of the stack with pi.

They also had some problems where if you did a function and then started entering digits it would overwrite the function result, but I think they fixed those. I've seen what I thought was that problem recently, but when I finished entering the number and hit enter or invoked a function on the number, the previous function result appeared second on the stack, so it apparently is just a bug in displaying the stack.

Re: What Is RPN? Why Did/Does HP Use RPN? Learning RPN (1999)

#45

Post by u801e » Sat, Mar 06, 2021, 9:37 PM UTC

I still have my HP 48g and I prefer using the dc[1] for calculations on my laptop.

[1] https://linux.die.net/man/1/dc

Re: What Is RPN? Why Did/Does HP Use RPN? Learning RPN (1999)

#46

Post by jonsen » Sat, Mar 06, 2021, 9:40 PM UTC

Algorithms for RPN Calculators by John A. Ball (1978) landed in my mailbox two days ago. It’s each and every detail you can imagine regarding RPN. Very well and thoruogh written. A great pleasure to study it:

https://www.amazon.com/Algorithms-RPN-calculators-John-Ball/...

Re: What Is RPN? Why Did/Does HP Use RPN? Learning RPN (1999)

#47

Post by bitwize » Sat, Mar 06, 2021, 9:40 PM UTC

There's an open-source Android app called Droid48 that gives you a virtual HP48, if you're into that sort of thing.

I know when I'm out with coworkers and they whip out Droid48 to calculate the tip, I picked a good place to work.

Re: What Is RPN? Why Did/Does HP Use RPN? Learning RPN (1999)

#48

Post by Aardwolf » Sat, Mar 06, 2021, 9:42 PM UTC

mtalantikite wrote: post #37

aseerdbnarng wrote: post #13

I was forced to use an HP12C as part of my university degree. Once you get used to RPN it’s quite uncomfortable to switch back. It’s a much more intuitive way to do math once you get over the small hurdle. 15 years later and I’m still using the same calculator!

For whatever reason my high school had HP48s for my junior year math class, which got replaced the following year for TIs since “that’s what you’ll be using in college”. I much preferred the RPN and ended up convincing my parents my life would be easier with a new HP49g (which wasn’t a lie, it was). That thing helped get me through my math major and I’ll always remember my old school professor who taught my complex a…

The HP48s has a much nicer keyboard than the HP49g though! HP48gx may have been a suitable upgrade instead :)

Re: What Is RPN? Why Did/Does HP Use RPN? Learning RPN (1999)

#49

Post by lloeki » Sat, Mar 06, 2021, 9:42 PM UTC

SavantIdiot wrote: post #33

aseerdbnarng wrote: post #13

I was forced to use an HP12C as part of my university degree. Once you get used to RPN it’s quite uncomfortable to switch back. It’s a much more intuitive way to do math once you get over the small hurdle. 15 years later and I’m still using the same calculator!

I bought an HP48 in 1990 junior year in college when it came out. A calculator WAS required for engineering school, but this one made everything way easier. I think it was almost $200. Anyway, once you go RPN, you don't go back. It makes way more sense. It finally died 5 years ago: the keys stopped working. I read about how to repair the keypad but finally had to let go. I had all my crib sheets from engineering scho…

Similar story. Got a 48GX in high school. Everyone had TI89, maybe TI-92. I was the only one with HP.

Even with its lowly Saturn CPU and perceptually slower, it was trouncing the TIs at basically every task, especially when you customised it.

I learned RPN and RPL alright, but also got to dive into System RPL: the low level, faster, much more rich RPL, but where every argument was basically unchecked as it was more like HP-provided ASM routines in disguise.

And then learned to bit-bang stuff on the screen in assembly with all the timing tricks to produce 4 grayscale instead of just black/white. Great for coding small games.

Got the the third party CAS algebra extension card that also replaced the original UI for the same thing, only faster and better, and with a much more potent symbolic solver, whose UI was absolutely glorious to write, select, navigate, and perform advanced stuff.

Also got a maxed out storage expansion for the second slot. Such storage was not solid state so it required a continuously operating CR2032 battery to persist over time.

Unfortunately, as robust as it was, some time after engineering school it took a hard fall too much and was irreparably broken.

Later got my hand on a HP49G+, ARM powered but surprisingly the default was to run an emulation of the Saturn CPU, and CAS was bundled. You could still code for the ARM one though. By that time I lost interest so it currently sits in a drawer. Also preferred the 48 boxy design, especially the mushy keys of the new one were way worse.

Re: What Is RPN? Why Did/Does HP Use RPN? Learning RPN (1999)

#50

Post by jeffbee » Sat, Mar 06, 2021, 9:44 PM UTC

tome wrote: post #41

ajarmst wrote: post #26

Earlier quoted context omitted.

Well, it’s easier to build because it has a terse syntax that requires fewer symbols, doesn’t need precedence and associativity rules, and has no ambiguous instructions. It’s easier to use for the same reasons.

> has no ambiguous instructions Really? What do you call an operator applied to an empty stack? A sequence of commands that leaves the stack non-empty? I don't see why that's any less ambiguous than mismatched parentheses.

Why would any person or machine care that the stack wasn't empty?