[Joker_vD]

> I discovered the pointer to the next line wasn't a good idea, because it needed to move every pointer after a line insertion.

Huh? Don't you need to only change the "next-line-pointer" for the line that's right before the inserted line?

> but the NEXT changed the line, but on the next statement it would lost track and get back to the line following the NEXT. The loops also require their own stack, but including the counter variable address, a pointer to the TO expression, and a pointer to the STEP expression (5 words in total).

Mmm. IIRC, usually the compiled NEXT statement would store the pointer to the corresponding FOR statement, so you don't need an additional stack for loop depth during the execution. But you still need it (or some other sort of chaining) during the program input so whatever.

> Typing the program was difficult, as the keyboard bounced a lot. This happens when you read too fast the keyboard, so fast you can see that effectively the key contact isn't perfect.

Yeah... I've read that keyboard microcontrollers has to deal with contact bounce even today.

[Someone]

> Mmm. IIRC, usually the compiled NEXT statement would store the pointer to the corresponding FOR statement, so you don't need an additional stack for loop depth during the execution

I think you do. Apart from common sense, nothing forbids one from writing stuff like

  100 for i = 1 to 10
  110 if i = 4 gosub 100
  120 print i
  130 next
  140 return

I think many basics also allowed changing that goto 100 to goto 200 and adding

  200 for j = 1 to 4
  210 print i
  220 print j
  230 next

Yes, things would likely end badly, but the basic interpreter would not be smart enough to reject such programs. Its editor didn’t even guarantee that a for statement had a corresponding next or vice versa; all it guaranteed was that the program consisted of a list of lines that each in isolation are valid basic code.

[egypturnash]

This is some beautifully horrible spaghetti, well done. It's like I'm eleven years old and barely understand what's going on in the computer again.

I just fired up VICE and my virtual c64 happily ran both of those, if throwing an "out of memory" error after about five runs through the first one counts as "happily".

[II2II]

> I discovered the pointer to the next line wasn't a good idea, because it needed to move every pointer after a line insertion.

I get the impression that they were storing everything sequentially in memory, rather than having a linked list of instructions. Why? I can only speculate. Perhaps it is to make memory management simpler (don't have to keep track of which addresses are in use), or to avoid memory fragmentation in system with limited memory (any modification of code would introduce unusable holes). If that's the case, what you want is an offset rather than an absolute address.

[Someone]

> I get the impression that they were storing everything sequentially in memory, rather than having a linked list of instructions. Why? I can only speculate.

I expect that’s because that is how ‘every’ homecomputer basic did it. Yes, that makes it slow to insert or remove a line close to the start of a long program, but it allow those offsets to be 8 bits, gaining a precious byte over a 16-bit absolute address.

Now, why they initially chose to waste those bytes? I wouldn’t know, but I guess that, because (FTA) “The CP1610 processor cannot address directly the internal memory in byte terms, instead everything is handled by full word”, they didn’t think of using a single byte.

[viraptor]

> Yeah... I've read that keyboard microcontrollers has to deal with contact bounce even today.

That will always be the case in hardware. The switch to on will be messy, for example like this:

https://makeabilitylab.github.io/physcomp/arduino/assets/ima...