75 lines
2.7 KiB
Markdown
75 lines
2.7 KiB
Markdown
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# Scope Reuse Blocks (MVP Proposal)
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Status: design-only during the feature‑pause (no implementation)
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Summary
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- Give short, reusable logic a name within the current scope without promoting it to a top-level function.
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- Keep the core small: block body + postfix header sugar; desugar to local function + normal calls.
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- Zero runtime cost: lowers to let/if/call/ret only (no new instructions/closures).
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Syntax (postfix header; Nyash style)
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- Block form (multi-statement):
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```nyash
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{ /* BODY */ } scope name(arglist?) (-> Ret)?
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// call within the same scope
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name(args)
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```
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- Expression form (one-liner):
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```nyash
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=> EXPR scope name(arglist?) (-> Ret)?
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```
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Semantics
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- Visibility: `name` is local to the defining scope; not exported.
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- Capture: by reference by default. Mutating captured vars requires explicit `mut` on those bindings.
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- Recursion: disallowed in MVP (can be lifted later).
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- Errors/exits: same as regular functions (return/cleanup/catch apply at the function boundary).
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Lowering (desugaring)
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- Transform into a local function plus a local binding for convenience calls.
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```nyash
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// { BODY } scope check(a:Int)->Str
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// ↓ (conceptual)
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let __cap_me = me; let __cap_locals = { /* needed refs */ };
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method __scope_check__(a:Int)->Str {
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return BODY
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}
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let check = (x) => __scope_check__(x)
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```
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- Captures are passed via hidden arguments or an environment box; no new VM opcodes.
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Examples
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```nyash
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{ if x % 2 == 0 { return "even" } return "odd" } scope parity(x:Int)->StringBox
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for i in range(0,10) {
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print(parity(i))
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}
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```
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Safety rules (MVP)
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- Capture: read-only by default; writes allowed only when the captured binding is declared `mut`.
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- Name uniqueness: `scope name` must be unique within the scope.
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- No cross-scope escape: values may be returned but the function reference itself is not exported.
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Observability & Tooling
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- Add trace toggles (design only):
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- `NYASH_SCOPE_TRACE=1|json` to emit enter/exit and capture lists as JSONL.
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- Example: `{ "ev":"enter","sid":42,"caps":["me","cfg","mut total"] }`.
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- Lints (design only):
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- Single-use scope → suggest inline.
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- Excess captures → suggest narrowing.
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Interactions
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- Works with guard/with/await sugars (it’s just a call).
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- Compatible with ASI and postfix aesthetics; no new top-level keywords beyond `scope` suffix.
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Tests (syntax-only smokes; design)
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- scope_basic: called twice → same result.
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- scope_capture_read: reads `me/foo`.
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- scope_capture_mut: mutation only allowed when `mut` is present.
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- scope_with_catch_cleanup: postfix catch/cleanup applied at local-function boundary.
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Pause note
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- This is documentation and design intent only. Implementation is deferred until after the feature‑pause (post‑bootstrap).
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