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@@ -1,12 +1,12 @@
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# Design — ISO exceptions for V3
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-**Status: M1–M5 complete (2026-10-23), tag `v3-exceptions`.** `EXCEPT`/
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-`RETRY`, the handler stack, `SYSTEM.THROW`, `EXCEPTIONS`, `M2EXCEPTION`,
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-`RETURN` unwinding, signal mapping, and compiler-emitted index/range/
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-CASE traps are implemented. `functionException`, `FINALLY`, coroutine/
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-protection exceptions and complex arithmetic remain follow-ups. Gates:
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-suite **276/276**, fixpoint OK **4,143,847 bytes**, corpus **512/612**
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-compile-OK, 0 crashes.
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+**Status: M1–M5 complete, plus the `functionException` follow-up
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+(2026-10-23), tag `v3-exceptions`.** `EXCEPT`/`RETRY`, the handler
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+stack, `SYSTEM.THROW`, `EXCEPTIONS`, `M2EXCEPTION`, `RETURN` unwinding,
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+signal mapping, and compiler-emitted index/range/CASE/function traps are
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+implemented. `FINALLY`, coroutine/protection exceptions and complex
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+arithmetic remain follow-ups. Gates: suite **278/278**, fixpoint OK
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+**4,156,434 bytes**, corpus **512/612** compile-OK, 0 crashes.
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The handoff calls this the largest remaining language feature. This
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document fixes the syntax, AST, runtime model, code-generation contract,
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@@ -533,9 +533,9 @@ through the existing external-procedure path.
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| --- | --- |
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| `indexException` | array index check; `FPE_FLTSUB` |
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| `rangeException` | subrange assignment/actual/`RETURN`/`INC`/`DEC`; set element; set span |
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-| `caseSelectException` | `CASE` no match, no `ELSE` (add explicit trap) |
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+| `caseSelectException` | `CASE` no match, no `ELSE` |
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| `invalidLocation` | `SIGSEGV`/`SIGBUS`, NIL/uninitialised pointer |
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-| `functionException` | function body ends without `RETURN` (follow-up; current V3 returns 0) |
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+| `functionException` | function body reaches its end without `RETURN` |
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| `wholeValueException` | `SIGFPE` integer overflow |
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| `wholeDivException` | `SIGFPE` integer divide-by-zero; optional negative divisor check |
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| `realValueException` | `SIGFPE` real overflow/underflow/invalid |
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@@ -577,11 +577,13 @@ Implemented in M1–M3 (`compiler/run_tests.sh`):
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`indexException`/`rangeException`.
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- `t_except_case`: no matching `CASE` label gives
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`caseSelectException`.
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+- `t_except_funcret`: a result function falling off its end raises
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+ `functionException`.
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+- `t_trap_funcret`: unhandled `functionException` aborts with rc 134.
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- `t_except_unhandled`: expect_trap (rc=134).
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- `t_retry_bad`: `RETRY` outside `EXCEPT` rejected with `237`.
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-`functionException` and real/complex/protection/coroutine detection are
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-still follow-ups.
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+Real/complex/protection/coroutine detection are still follow-ups.
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Use `expect_run_files` with:
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@@ -613,8 +615,8 @@ cd .. && TMP="$PWD/.scratch/fixpoint" ./bootstrap/fixpoint.sh
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tools/v3-corpus/corpus.sh
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```
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-Current M4 gates: suite **276/276**, fixpoint OK
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-**4,143,847 bytes**, corpus **512/612 compile-OK**, 0 crashes.
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+Current gates: suite **278/278**, fixpoint OK
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+**4,156,434 bytes**, corpus **512/612 compile-OK**, 0 crashes.
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Existing trap tests must stay rc=134.
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---
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@@ -645,8 +647,8 @@ Existing trap tests must stay rc=134.
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`INDEX.md`; tag `v3-exceptions` at the M4 commit and a session-end
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tag at the docs commit.
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-`functionException`, real/complex/protection/coroutine detection can
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-follow separately; they should not block M1–M4.
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+Real/complex/protection/coroutine detection can follow separately;
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+they should not block M1–M4.
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---
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@@ -669,9 +671,6 @@ follow separately; they should not block M1–M4.
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needs its own design.
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- **Coroutines:** the state/handler stack is global, not per-coroutine.
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`coException` remains undetected.
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-- **Function result:** current V3 returns 0 when a function falls off
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- the end; raising `functionException` is a follow-up because it can
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- change existing behaviour.
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- **Separate compilation:** the runtime ABI (`m2_exc_*`) is stable, but
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per-unit exception tables/handler metadata would be needed once
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objects are separate. Not part of this milestone.
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@@ -689,6 +688,3 @@ follow separately; they should not block M1–M4.
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initialization/finalization). Proposed: yes.
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3. Decide the exact `THROW(i)` mapping when `i` is outside
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`0 .. 14` (proposed: `exException`).
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-4. Confirm whether `functionException` should be raised now for
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- functions with a handler whose body/handler falls through without
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- `RETURN`; proposed: follow-up, not M1.
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