c8063c9e41
net-plugin: modularize constants (consts.rs) and sockets (sockets.rs); remove legacy commented socket code; fix unused imports mir: move instruction unit tests to tests/mir_instruction_unit.rs (file lean-up); no semantic changes runner/pyvm: ensure using pre-strip; misc docs updates Build: cargo build ok; legacy cfg warnings remain as before
89 lines
3.7 KiB
Markdown
89 lines
3.7 KiB
Markdown
Exception Handling — Postfix catch / cleanup (Stage‑3)
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Summary
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- Nyash adopts a flatter, postfix-first exception style:
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- try is deprecated. Use postfix `catch` and `cleanup` instead.
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- `catch` = handle exceptions from the immediately preceding expression/call.
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- `cleanup` = always-run finalization (formerly finally), regardless of success or failure.
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- This matches the language’s scope unification and keeps blocks shallow and readable.
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Status
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- Phase 1: normalization sugar（既存）
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- `NYASH_CATCH_NEW=1` でコア正規化パスが有効化。
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- 後置フォームは内部 `TryCatch` AST に変換され、既存経路で降下。
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- 実行時コストはゼロ（意味論不変）。
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- Phase 2（実装済み・Stage‑3ゲート）
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- パーサが式レベルの後置 `catch/cleanup` を直接受理。
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- ゲート: `NYASH_PARSER_STAGE3=1`
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- 糖衣正規化はそのまま併存（関数糖衣専用）。キーワード直受理と二重適用はしない設計。
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Syntax (postfix)
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- Expression-level postfix handlers (Stage‑3):
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- `expr catch(Type e) { /* handle */ }`
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- `expr catch { /* handle (no variable) */ }`
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- `expr cleanup { /* always-run */ }`
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- Combine: `expr catch(Type e){...} cleanup{...}`
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- Method/function calls are just expressions, so postfix applies:
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- `call(arg1, arg2) catch(Error e) { log(e) }`
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- `obj.method(x) cleanup { obj.release() }`
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Precedence and chaining
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- Postfix `catch`/`cleanup` binds to the immediately preceding expression (call/chain result), not to the whole statement.
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- For long chains, we recommend parentheses to make intent explicit:
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- `(obj.m1().m2()) catch { ... }`
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- `f(a, b) catch { ... } cleanup { ... }`
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- Parser rule (Stage‑3): postfix attaches once at the end of a call/chain and stops further chaining on that expression.
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Diagram (conceptual)
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```
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// before (parse)
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obj.m1().m2() catch { H } cleanup { C }
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// precedence (binding)
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obj.m1().[ m2() ↖ binds to this call ] catch { H } cleanup { C }
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// normalization (conceptual AST)
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TryCatch {
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try: [ obj.m1().m2() ],
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catch: [ (type:Any, var:None) -> H ],
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finally: [ C ]
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}
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```
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Normalization (Phase 1)
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- With `NYASH_CATCH_NEW=1`, postfix sugar is transformed into legacy `TryCatch` AST:
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- `EXPR catch(T e){B}` → `TryCatch { try_body:[EXPR], catch:[(T,e,B)], finally:None }`
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- `EXPR cleanup {B}` → `TryCatch { try_body:[EXPR], catch:[], finally:Some(B) }`
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- Multiple `catch` are ordered top-to-bottom; first matching type handles the error.
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- Combined `catch ... cleanup ...` expands to a single `TryCatch` with both blocks.
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- Lowering uses the existing builder (`cf_try_catch`) which already supports cleanup semantics.
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Semantics
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- catch handles exceptions from the immediately preceding expression only.
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- cleanup is always executed regardless of success/failure (formerly finally).
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- Multiple catch blocks match by type in order; the first match is taken.
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- In loops, `break/continue` cooperate with cleanup: cleanup is run before leaving the scope.
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Migration notes
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- try is deprecated: prefer postfix `catch/cleanup`.
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- Member-level handlers (computed/once/birth_once/method) keep allowing postfix `catch/cleanup` (Stage‑3), unchanged.
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- Parser acceptance of postfix at expression level will land in Phase 2; until then use the gate for normalization.
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Examples
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```
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// Postfix catch on a call
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do_work() catch(Error e) { env.console.log("error: " + e) }
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// Always-run cleanup
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open_file(path) cleanup { env.console.log("closed") }
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// Combined
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connect(url)
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catch(NetworkError e) { env.console.warn(e) }
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cleanup { env.console.log("done") }
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// Stage‑3 parser gate quick smoke (direct acceptance)
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// NYASH_PARSER_STAGE3=1 ./target/release/nyash --backend vm \
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// apps/tests/macro/exception/expr_postfix_direct.nyash
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```
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