Compile-time evaluation sits beside capability access, without a termination proof

[TheLazyCat00]

Brings the spec in line with compile-time evaluation as the compiler now does it (zane-lang/compiler#184, closing zane-lang/compiler#163). Following review, the spec states the language property that makes compile-time evaluation possible, not the compiler's algorithm.

Spec

• effects.md §5.3, new: compile-time evaluation. A verb receives what it works with through its parameters and capability-backed state. So the compiler may evaluate at compile time any computation that depends on neither, or leave it for run time. Doing so never changes what a program prints or computes. The section comes right after §5.2, the capability rule it rests on.
• effects.md §5.2 is now "Capability access". Termination is no longer a derived fact. Capability access is the only one, and it decides compile-time evaluation (§5.3) and parallelism. The old §5.3 and §5.4 become §5.4 and §5.5, and a summary row is added.
• concurrency.md §2 keeps implicit parallelism only. The old §2.1 and §2.3 on compile-time reduction are gone. §2.1 "Parallelization of independent work" says a call may run in parallel whether or not it terminates. Thread configuration becomes §2.2.
• contributing/writing-spec-docs.md §3.6, new. Compiler behaviour that a language rule enables is stated next to that rule, as what the compiler may do and what that guarantees, never how it does it. Not every compiler behaviour belongs in the spec.

The leaves-up evaluation, the work bound and replaying outputs are compiler details. They live in the compiler's docs/design/optimization.md (zane-lang/compiler#187).

Story

• New final chapter in stories/effects.md: "Compile-time evaluation needs no termination proof and sits beside capability access". It covers:
  • why termination and the capability condition fell while building the evaluator;
  • why the first draft read as a compiler spec;
  • why implicit parallelism kept the result in the spec rather than out of it;
  • the cost of these choices.
• Supersession notes on the five earlier passages in stories/concurrency.md and stories/effects.md that claimed compile-time evaluation needs termination or the three conditions. Two existing notes are corrected to drop termination as a derived fact.

Checks

• npx markdownlint-cli2 "**/*.md" is clean.
• Every guard grep in CLAUDE.md comes back empty.
• git diff --word-diff origin/main -- stories/ shows published chapters changed only by supersession notes.

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📝 Walkthrough

Walkthrough

The specifications and stories revise compile-time reduction and capability-analysis rules. Reduction applies to known-input computations within a work bound, preserves writes in order, and leaves specified computations as runtime work. Capability access, rather than termination, is the derived fact used to govern compile-time evaluation and parallelism.

Changes

Compile-Time Reduction

Layer / File(s)	Summary
Capability access rules spec/effects.md, stories/effects.md	The effects specification now identifies capability access as the derived fact. It retains assumptions that unknown callees may read and write capability-backed state.
Bounded compile-time reduction spec/concurrency.md, stories/concurrency.md, stories/effects.md	The documents describe reduction from known-input computations within a work bound. They specify ordered replay of writes, runtime work that remains unreduced, and parallelization without a termination requirement in the stated cases.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Other

Merge Risk: 🔵 Low · up to 0833d

The story’s explanation overstates when known-input computations are reduced. Clarify the work bound before merging so readers are not misled about compile-time behavior.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
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Title check	✅ Passed	The title identifies the change to compile-time evaluation and the removal of the termination-proof requirement, which are central to the pull request.

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Code Review

This pull request updates the Zane language specification and design stories to redefine compile-time reduction. Instead of requiring a formal proof of termination, the compiler now performs reduction from the leaves up within a bounded work budget, removing termination as a derived effect. The review feedback suggests a minor correction in the design story document to use the British spelling 'analyse' instead of 'analyze' for consistency with the rest of the repository.

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Actionable comments posted: 1

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Inline comments:
Review comments at @stories/effects.md:
- Line 111: Revise the superseded note about compile-time folding to qualify
reduction of known-input computations by the work bound: computations exceeding
the bound remain at runtime. Preserve the reference to “Compile-time reduction
runs from the leaves up, within a bound on work.”

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[TheLazyCat00]

to me this reads more like a specification. tbh i dont even think this should be in any concurrency documents. furthermore, it should be reconsidered whether the spec really should specify compiler implementation details, including optimization. if the spec is the right place, then it should go into a dedicated file, for example compiler.md or optimization.md. the reason this doesnt read like a story is because it states facts, not reasoning

[TheLazyCat00]

Agreed on both counts. The story chapter lists conclusions instead of telling how we got to them, and §2.1/§2.3 describe what the compiler does, not what the language is. Before I rewrite anything, here's the placement fork:

A. Take compile-time reduction out of the spec (my recommendation). Reduction doesn't change anything a program can observe, so the language doesn't need to describe it. All the spec needs is the one guarantee every optimization shares: the compiler may transform a program in any way that changes neither what it prints nor what it computes, only how fast it runs. That's one sentence, in foundations.md or wherever the guarantee is stated. Concretely:

• concurrency.md §2.1 and §2.3 go.
• effects.md §5.2 keeps capability access only as the fact parallelism uses.
• The reduction design lives where it already does, in the compiler's docs/design/optimization.md.

B. A dedicated spec/optimization.md (or compiler.md). It would hold the reduction rule plus that guarantee, with its own story file. This keeps reduction normative, but it puts implementation choices (the bound, what counts as an input) into the spec, which is what you're questioning.

Either way, the story gets rewritten as reasoning: the actual sequence of what pushed us off the three-condition rule while building it. Under A, that chapter also says why reduction left the spec. Since concurrency.md is where the rule lived, the chapter stays in stories/concurrency.md unless you'd rather put it in stories/foundations.md.

One related question: implicit parallelism (concurrency.md §2.2) is also an unobservable compiler optimization. Should it go out with reduction, or stay? It's part of how §1 explains the split between parallelism and spawn, so I'd lean towards keeping it and touching only reduction in this PR.

Which way do you want it?

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[TheLazyCat00]

i was about to comment a until i got to your implicit parallelism note. it is worth discussing as it reshaped my reasoning. implicit parallelism is a very rare language feature (i dont know any languages that do this). so i think it is worth mentioning somewhere. it is also not a compiler optimization in the sense that "while writing the compiler we quickly implemented this optimization". it is tightly coupled with the language semantics, which is why it is so hard to move it somewhere else. i dont know what's best yet, so i'll just share my thoughts before deciding

[TheLazyCat00]

That changes my view of A too. I think it separates two things that both sit in §2 today:

• What the language guarantees, which makes the optimization possible. Implicit parallelism exists because effects are structural: a verb's kind says what it may write, capabilities are explicit, and spawned mutation needs a value subject, so the compiler can prove two pieces of work independent. Reduction rests on the same base: every input reaches a verb through a parameter or a capability, so the compiler can tell which computations depend only on values it knows. That's a property of the language, it's rare, and it belongs in the spec, as you say.
• How a compiler uses it. Reducing from the leaves up, the work bound, replaying outputs, profitability heuristics for parallelism. That is implementation and belongs in the compiler's docs.

So a third option:

C. Keep both in the spec, stated as language properties, not algorithms. Each gets the guarantee that makes it possible, plus the rule that it can't be observed. Parallelism stays in concurrency.md, since it's half of the parallelism/spawn split. Reduction isn't about concurrency, so it would move out, either to effects.md §5 ("What the compiler derives"), which already holds the capability fact it depends on, or to a new file if you'd rather keep "what the language lets a compiler do" in one place. Either way it shrinks to a couple of sentences: the compiler may evaluate at compile time any computation that depends on no parameter of its verb and on no capability-backed read. It may leave any such computation for run time, and evaluating one never changes what a program prints or computes. Leaves-up, the bound and replay move to docs/design/optimization.md.

The story chapter would then tell how we got there: building it showed that the old three conditions were the compiler's bookkeeping, and that the language only needs to guarantee what makes reduction possible.

No rush. Tell me when you've decided and I'll rewrite.

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[TheLazyCat00]

i think the best is option c, as you proposed, but with the important rule that not all compiler details have to be written down and that the compiler stuff that should be mentioned sit right after the section that enables that compiler behaviour. this makes the spec spec-first again and allows the freedom to mention unique things

[TheLazyCat00]

Done in 31ad50a (spec) and 9f1aecf (story):

• effects.md §5.3, compile-time evaluation, sits directly after §5.2, capability access, the rule it rests on. It says which computations may be evaluated at compile time (those that depend on no parameter and no capability-backed read) and that doing so is unobservable. It leaves out leaves-up evaluation, the bound and replay, which stay in the compiler's docs.

• concurrency.md §2 keeps only implicit parallelism. Its §2.1 and §2.3 on reduction are gone.

• Your rule is now contributing/writing-spec-docs.md §3.6. A behaviour a rule enables is stated next to that rule, as what the compiler may do and what that guarantees, never how. It also says that not every compiler behaviour needs a mention.

• The story chapter moved to the end of stories/effects.md, next to the rule it explains, and is rewritten as reasoning:

  • why termination fell;
  • why the capability condition was drawn too wide;
  • how the first draft turned into a compiler spec;
  • why implicit parallelism kept the result in the spec instead of out of it.

  Please check that the order of events matches how you saw it.

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