4 ms·

Not OP, but as a fellow Lisp-on-wasm developer one problem is that the current release doesn't support tail call elimination. There's a proposal for it (a tail_

Not OP, but as a fellow Lisp-on-wasm developer one problem is that the current release doesn't support tail call elimination. There's a proposal for it (a tail_call instruction), and Chrome has implemented it, but the Firefox/Spidermonkey team hasn't prioritized it, so it's sat for a couple years. At least two implementations (maybe two browser implementations? I don't recall) are needed for standardization, so things remain. You know, I wonder how seriously I could be taken if I duck-taped a wasm-capable browser together out of Servo and Wasmtime to make a second implementation and push it forwards...

gumby 4y ago
There is no branch instruction at all?
- miloignis 4y ago
  There is, but all control flow is structured and the argument/return address stack is out of your control. You have blocks, loops, and if/else statements. The behavior of a branch instruction differs based on context - in a block, it jumps out of the block, in a loop it jumps to the beginning of the loop. If you really wanted full tail-call behavior, you would either have to compile every function into the same mega-function in a loop and have some sort of if/else tree, or use trampolines (which would additionally require either storing parameters in memory somewhere or using the same type signature for all functions, since function calls are typed). Overall, it's not a super great situation for true tail-call elimination. For now, I've implemented limited tail-call elimination for single-function recursive calls (transforming them into an in-function loop), and that's patched things up enough for me to continue working for now until I either need to come up with an optimized trampoline or the tail_call instruction finally gets standardized.
  - gumby 4y ago
    Thanks, that is pretty dreadful.
    - metagame 4y ago
      The spec people have been very rude to the Lisp people every time something has been brought up. I'm not going to look up everything that's been written, but here's an example: https://sourceforge.net/p/sbcl/mailman/message/34821303/ https://sourceforge.net/p/sbcl/mailman/message/34821303/
      - aidenn0 4y ago
        I wouldn't call their responses rude, but they are somewhat dismissive.

gumby 4y ago

There is no branch instruction at all?

miloignis 4y ago
There is, but all control flow is structured and the argument/return address stack is out of your control. You have blocks, loops, and if/else statements. The behavior of a branch instruction differs based on context - in a block, it jumps out of the block, in a loop it jumps to the beginning of the loop. If you really wanted full tail-call behavior, you would either have to compile every function into the same mega-function in a loop and have some sort of if/else tree, or use trampolines (which would additionally require either storing parameters in memory somewhere or using the same type signature for all functions, since function calls are typed). Overall, it's not a super great situation for true tail-call elimination. For now, I've implemented limited tail-call elimination for single-function recursive calls (transforming them into an in-function loop), and that's patched things up enough for me to continue working for now until I either need to come up with an optimized trampoline or the tail_call instruction finally gets standardized.
- gumby 4y ago
  Thanks, that is pretty dreadful.
  - metagame 4y ago
    The spec people have been very rude to the Lisp people every time something has been brought up. I'm not going to look up everything that's been written, but here's an example: https://sourceforge.net/p/sbcl/mailman/message/34821303/ https://sourceforge.net/p/sbcl/mailman/message/34821303/
    - aidenn0 4y ago
      I wouldn't call their responses rude, but they are somewhat dismissive.