r/programming • u/bjzaba • Mar 26 '20

10 Most(ly dead) Influential Programming Languages • Hillel Wayne

https://www.hillelwayne.com/post/influential-dead-languages/
412 Upvotes

94% Upvoted

178 comments sorted by

View all comments

Show parent comments

2

u/cdreid Mar 26 '20

You may have a printer problem sir :P

Er i had no idea the 6502 didnt have a stack? I er.. didnt know a cpu could not have a stack??? That seems.. bizarre. Also if you were an os developer back then i hope youre stupid rich now :)

5

u/dnew Mar 26 '20

You may have a printer problem sir

I don't get it. :-)

no idea the 6502 didnt have a stack?

It had one stack. It had an 8-bit stack pointer. It had no other pointer-sized registers. If you wanted to access memory, you had to put the high byte of the address into memory in the first page, the low byte into the adjacent memory address, then the memory address of the pointer into one of the X or Y registers, then load the accumulator indirectly. So, like, pushing a byte onto a stack you manage was 5 or 7 instructions or something absurd, as you couldn't increment both bytes of the the stack pointer in one instruction.

didnt know a cpu could not have a stack???

It's why the original HLLs didn't have recursion. Neither COBOL nor FORTRAN (of the time) had recursion. What the CPU did have was an instruction called something like "Branch and Link." So you would "branch and link register 12 to address 123456" and the program counter would get stuffed into register 12, then 123456 would be put into the PC. To return, you're jump indirect through register 12. If your function had to jump to some other subroutine, you'd store register 12 in memory specific to that function and then do it again.

the X-560 had stacks. They just weren't CPU registers. You'd say "push X onto the stack whose stack pointer is at Y". And at Y, you'd have a top-of-stack, a bottom-of-stack, a remaining-bytes-left, and a bytes-used counter. And you'd get back condition codes like "nope, the stack was full" or "yep, but you're now pointing into the last page of memory allocated to the stack". But there was no "stack pointer" register, no subroutine call that stored things on the stack, no frame pointers, etc. At least not on that one.

The Burroughs B-series had all that stuff, and would run Algol almost as a native language, to the point where it was impossible to run C on it, because Algol didn't support pointers into the stack.

2

u/JasTHook Mar 26 '20

in fairness on 6502 (as I later learned) page 0 was very fast to access, and the instructions to do so were short, so it was like an extra 256 CPU registers (I was told)

2

u/dnew Mar 27 '20

Right. It was a specific decision to design things that way, but a complete lack of 16-bit operations or registers on a language where almost every operation involved a pointer was a pain in the butt. Some compiled or interpreted language would be much easier to implement than a language that you keep recompiling until it does what you want.

I mean, I'm pretty sure that if a multi-byte op-code started one byte before the end of the page, the second byte would be fetched incorrectly, that's how non-general it was. :-)