Disappointed, I set out to fix it. Voila!
A Brainfk interpreter in pure Google Sheets formulas. The hard part was parentheses matching, so I think other VMs would be even easier.
So you did kind of a functional style where each row represents an instruction being run with a full copy of the state of the VM at that point in time. Then each subsequent row is based on the state of the previous one. Am I reading that right? (I'm not familiar with Brainfk)
The more interesting hackery is in the parenthesis parser...
First, lets split the code to one char per row:
Now, lets parse `[` as 1, `]` as -1, anything else as 0:
Now for the i'th row of the "] match" column, lets find the index of the first 0 in the i'th column, and add `i-1` to get an index from the beginning of the code instead of from the opening bracket:
Voila! Column B now contains for every bracket its matching bracket's index in the code, and for anything else, "".
A comment about how you have presented this - not everything has to be an interesting technical accomplishment.
Creating beginners is a much harder skill and topic than most realize.
Making topics easy to approach and learn is often much harder than learning the technical topic.
Impressive how quickly you whipped this up
It's just that I clicked hoping for one thing and found another, so I felt a need to show that the second one is also doable :-)
Also, it took me more than I expected. I had to go through a couple of wrong approaches and some confusion until I figured out bracket matching, and also had a bug or two that took a while to debug in the interpreter table. These things aren't hard to make! Try it sometime :-)
Would love to learn and chat a bit more about your previous startup (I see you have posted below and will reply there).
It started with a programming course I founded for data analysts in my army unit that taught them enough Python and sql and requests and win32com to be able to automate significant parts of their own jobs, creating a lot of value, and I wanted to figure out how to teach the same course outside.
The answer was "nobody outside the army knows how to deal with losing an employee for 3 weeks", so we cut the material again and again and even at the minimum we could reach - 80 hours - we couldn't make a single sell.
So my cofounder quit and I started playing with different models of teaching, and found out that there are huge benefits to teaching with a computer game (more fun, more engaging, more self-driven, but mostly - you get so much data and can optimize your lessons so fast... I really don't understand why e.g. Codecademy don't do a lot more data-based micro-optimization).
I partnered with some people that sold after-class activities to middle schools and we sold a lot more courses than we planned, so I had a frantic year of supervising the teaching of 14 courses while trying to amend my weekend prototype to teach the whole material. On the way I developed a bunch of other nice teaching activities.
But working alone sucked, so I put it on hold and went looking for the best team I could find for my "real" startup (this one was started with the explicit intention of failing but learning as much as I can, as I was pretty clueless in business at the time).
I strongly believe in educational technology as an efficient way to improve the world (though a bit less than I use to as a way to get rich). I fully intend to return to working in the field when I'm no longer needed at FeezBack (sorry, again we're Israel-only at the moment, so no links).
I would say that the original submission illustrates much better how simple a CPU is. And it actually exposes the user to syntax (ASM) and concepts (program counter, registers, memory usage, stack, etc) that directly transfer to basic CPU design. Your version, while technically more impressive, buries this under formulas and the particulars of parsing a language nobody uses.
FWIW, I agree with j45 that you presented this poorly. From being "disappointed" and "fixing" another user's submission, to your token parenthetical (in which you actually did not "make sure" to say it was "very impressive"). It all seems a bit condescending and arrogant for someone who would be an educator. Compare the tone and demeanor of his comments on your submission (positive, supportive) to yours on his (negative, critical).
I've used Brainfuck in some educational contexts (like the talk on virtual machines that I gave in PyCon IL a few weeks ago and in a local python meetup before that), although not yet with complete beginners.
It's useful in some contexts and not others. It's especially useful when some of your audience has heard of it before.
It's especially useful because it lets me mention other "war stories", like this one (students love war stories): https://news.ycombinator.com/item?id=7943514
Before I teach asm, I always take 1.5 hours to teach an exercise I once developed called the "shirts exercise", which is about optimizing code for a simple and very intuitive vm that looks a lot less like real asm than Brainfuck does (for example, it has conservation of material). Real asm has so much incidental complexity and I prefer to show the beauty and motivation for learning it before we start learning about number encoding etc'.
The reason to use this spreadsheet is that it's written in a format that my students would be able to follow and understand. So if I tell them "this is exactly how a computer is built", I hope to demistify a bit the idea of a computer. A good programmer is a programmer that is not afraid to dig into abstractions.
I don't feel you were overharsh, you justifiably called my bullshit, which is an important thing to do once in a while.
Re: Brainfuck in education, it's not about unfamiliarity, it's about time-to-grasp-core-idea, and number-of-other-ideas-you-need-to-understand-first. You really want to minimize those.
Specifically in teaching asm, you want your students to reach as fast as possible the state where they completely wrap their head about all the details and edge cases of the machine. Brainfuck is a really simple machine, very easy to hold completely in your head. Even the simplest RISC processor that can do anything real would require you to first understand binary, hex, two's complement, the idea and implementation of a stack, and so many more things...
For another example see this Twitter discussion between David Beazly, Aaron Meurer and myself on the subject of teaching TDD to complete beginners: https://twitter.com/dabeaz/status/879487816538914817
I can see where using Brainfuck would have its advantages, sometimes that unfamiliarity can help you focus on the underlying abstractions rather than the syntax.
Then you can read the writeup I wrote in response to another commenter (the guy who wrote the original Apps Script VM).
So if you go to the orange section of the sheet you see where the program state is displayed. Each row represents the state of the program at that point. The "Out" column is the stack represented as ASCII characters. The "Cursor" column is the stack pointer. The "IP" column is the instruction pointer (which instruction you're currently looking at). The "Instruction" column is the instruction being done at that point in time. The "Cells" column is the stack displayed from left to right.
I may be a little off but that is the general idea.
Replace the word "stack" with "memory buffer" or "tape" everywhere. "Out" represents STDOUT, there is the "." command for printing (and "," for reading from STDIN).