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Yes, tail calls are essential to the current formulation of the operational semantics. If you break it then e.g. a loop will no longer run in constant space but blow the stack. Other constructs like blocks and The loop issue could be avoided by implementing it with a loop instead of a tail call, but of course that would no longer be declarative, i.e., "speccy". Maybe that's okay in this isolated case. The linearity in nesting depth could not be avoided, however. |
Connicpu
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May 11, 2020
* add syntax highlighting * Update Overview.md
Connicpu
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dhil
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This updates the explainer text according to the new spec we agreed in the 09-15-2020 CG meeting and discussions afterwards. The following are modifications and clarifications we made after the 09-15-2020 CG meeting, and the relevant issue posts, if any: https://github.com/WebAssembly/meetings/blob/master/main/2020/CG-09-15.md - `catch_br` wasm renamed to `delegate` (WebAssembly#133) - `rethrow` gains an immediate argument (WebAssembly#126) - Removed dependences on the reference types proposal and the multivalue proposal. The multivalue proposal was previously listed as dependent because 1. `try` is basically a `block`, so it can have multivalue input/output 2. `br_on_exn` can extract multiple values from a `block`. We don't have `br_on_exn` anymore, and I'm not sure 1 is a strong enough reason to make it a dependence. - Mention `rethrow` cannot rethrow exceptions caught by `unwind` (WebAssembly#142 and WebAssembly#137) - Mention some runtimes, especially web VMs, can attach stack traces to the exception object, implying stack traces are not required for all VMs - Update label/validation rules for `delegate` and `rethrow` (WebAssembly#146) - Finalize opcodes for `delegate` (0x18) and `catch_all` (0x19) (WebAssembly#145 and WebAssembly#147) I believe this resolves many previous issue threads, so I'll close them. Please reopen them if you think there are things left for discussions in those issues. Resolves WebAssembly#113, resolves WebAssembly#126, resolves WebAssembly#127, resolves WebAssembly#128, resolves WebAssembly#130, resolves WebAssembly#142, resolves WebAssembly#145, resolves WebAssembly#146, resolves WebAssembly#147.
alexcrichton
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Sep 19, 2025
Pass on instruction syntax
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This PR isn't ready as-is; I'm just looking for feedback.
I've found this debugging feature, which which prints out all values of all operations as they are executed, to be quite handy. The patch here could be prettier, and it'd be nice to print the opcode too, but my main question is: This patch breaks the "tail call" property of eval_expr, which was mentioned a while ago as an important property; is there a convenient way to do what this patch is doing with doing that?