hakorune/docs/papers/result_mode_exceptions.md

Structured Exceptions via Result‑Mode (Draft)

Problem

• Language exceptions are hard to implement portably (unwinding, landing pads) and complicate SSA/CFG.

Contribution (Nyash)

• Express try/catch/cleanup with Result‑mode lowering (no MIR Throw/Catch): structured blocks and jumps.
• Thread‑local ThrowCtx to aggregate nested throw to a single catch.
• PHI‑Off: merge variables via edge‑copy; harness synthesizes PHIs.
• Block‑Postfix Catch syntax: { body } catch (e) { … } [cleanup { … }] with single‑catch policy.

Method

• Parser (gated): accept try/throw + postfix catch, normalize to ASTNode::TryCatch.
• Bridge: set ThrowCtx on try entry; route throw to catch BB; bind catch param via incoming.
• Cleanup: always runs; merge at exit with PHI‑off rules.

Code References

• Parser: src/parser/statements.rs
• Bridge lowering: src/runner/json_v0_bridge/lowering/{try_catch.rs, throw_ctx.rs}
• Smokes: tools/test/smoke/bridge/try_result_mode.sh

Evaluation Plan

• Semantic parity: PyVM vs. harness binaries on representative cases.
• Control‑flow complexity: nested if/loop + cleanup; ensure merges are stable.

Reproduce

• bash tools/test/smoke/bridge/try_result_mode.sh