# Next session — plan (from 2026-10-23)

**Branch:** `master`.  **Feature state:** `v3-exceptions` + `v3-ptrchain` + `v3-function-exception` + `v3-finally` + open-array M1/M2/M3.
**Gates:** suite **292/292**, fixpoint **OK (3,453,395 bytes)**,
corpus **518/612, 0 crashes**.

Read first: `docs/STATUS.md`, `docs/features.md`,
`docs/gaps/README.md`, `docs/summary_session-2026-10-23-exceptions.md`.

## Policy reminder

V3 follows **PIM/ISO Modula-2**, not gm2 leniencies.  Declaration before
use is required for data; only a `POINTER`'s base may forward-reference.
gm2 compatibility is accepted only where documented in `docs/gaps/`.

## 1. `PACKEDSET` — done (spans ≤ 32 bits)

Implemented 2026-10-23: 1/2/4-byte storage, `SIZE`/`ORD`, `INCL`/`EXCL`/
`IN`, assignment, set operations, packed arrays/records/parameters.
Wider packed sets are a loud `230` implementation limit.  Regression
`t_packedset`.

The corpus files `onebyte`, `onebyte2`, `onebyte3` still **do not
compile**, but the blocker is earlier: they use the module variable `r`
inside `assert` before its declaration (declaration order, rejected by
policy).  With `r` moved before the procedure they compile and run.
Do not relax declaration order for this corpus case.

## 2. ISO exceptions — done (`v3-exceptions`)

A dedicated feature session, not a small fix.  The design is in
`docs/design-exceptions.md` (grammar/AST, handler stack, `sigsetjmp`/
`siglongjmp` codegen, `EXCEPTIONS`/`M2EXCEPTION`, trap mapping, tests).

**M1 parser/AST — done (2026-10-23).**  `EXCEPT`/`RETRY` are reserved
words; bodies carry `NkExcept`/`NkRetry`; `RETRY` outside a handler is
error **237**.

**M2 runtime/codegen — done (2026-10-23).**  Handler stack + saved
state, `m2_exc_push`/`leave`/`retry`/`raise`, `sigsetjmp` dispatch,
`EmitRet` pops, `m2_exc_init` in `main`, `SYSTEM.THROW`, and basic
`SIGSEGV`/`SIGFPE` mapping.  Positive tests: `t_except_parse`,
`t_except_throw`, `t_except_retry`, `t_except_return`,
`t_except_nested`, `t_except_module`, `t_except_signal`; negative
`t_retry_bad` (237).

**M3 libraries — done (2026-10-23).**  `SysExceptions`,
`EXCEPTIONS` and `M2EXCEPTION` are implemented in
`runtime/syslib/SysExceptions.*` and `stdlib/{exceptions,m2exception}.*`.
`t_except_lib` covers `RAISE`, `CurrentNumber`, `GetMessage`,
`IsCurrentSource`, `IsExceptionalExecution`, wrong-source `exException`,
and `M2Exception` after `SYSTEM.THROW`.

**M4 language traps — done (2026-10-23).**  `TrapCode`, `CheckIndex`
vs `CheckRange`, CASE `caseSelectException`, and unhandled-exception
abort (rc 134).  Tests: `t_except_trap`, `t_except_case`,
`t_except_unhandled`.

**M5 finalization — done (2026-10-23).**  Session summary
`summary_session-2026-10-23-exceptions.md`; feature tag
`v3-exceptions` at `02b3763`, session-end tag at the docs commit.
Optional follow-ups: coroutine/protection exceptions.

**Corpus reality:** `lazyunique` now compiles and runs (`rc=0`,
unique output `0, 2, 1`) after the pointer-chain follow-up; the corpus
count stays **512** because it was already compile-OK.  Regression
`t_ptrchain` covers the self-referential record layout and
`p^.next^.value` path.  `except2/4/5/7/8/9` still fail declaration
order because `ip` is declared after the procedures, like `onebyte*`;
keep moved-`ip` copies as semantic tests but do not count them in the
corpus until the policy changes.

## 3. Multi-dimensional open arrays — design ready

See `docs/design-open-arrays.md`.  Chosen ABI: **per-level view
descriptors over one contiguous flat backing block**, with payload
`SIZE`/`ADR` semantics for multi/open arrays.  Full scope: fixed/open
2-D and 3-D, `VAR`, subarray views, row → 1-D, 2-D → `ARRAY OF BYTE`,
records/constructors.

**M1 — type/ABI helpers — done (2026-10-23).**  `ArrayRank`,
`IsMultiArray`, `ArrayLeafBytes`, `ArrayStride`, `ArrayPayloadSize`;
`MaxDefer` 512 and the session SSA buffer 8 MiB.

**M2 — fixed multi storage — done (2026-10-23).**  Static and local
rank-2/3 arrays now use one contiguous payload plus a chain of 40-byte
views `{count, elemBytes, stride, base, next}`.  `ViewIndex` yields
subviews or final element addresses; pointer-to-multi indexing and
`NEW`/local initialization work.  Whole-array copies handle new views
and old nested static constructors (`CopyOldNestedToView`).  A temporary
copy-in/copy-back adapter maps rank-1 row views to the legacy 1-D
descriptor for fixed/open formals; this was required by the compiler's
own `files[n]`/`symSet[...]` uses and is not the final M3 ABI.
Multi-dimensional record fields still use the legacy nested layout;
`t_nestarr` is unchanged.  Regression `t_multidim_local` was added.
Suite **284/284**, fixpoint **OK**, corpus **512/612, 0 crashes**.

Corpus: `unbounded`, `unbounded2/3/4/6/8`, `array9`, `adrunbounded3`.
Do not just accept the files; the ABI and `ADR(m) = ADR(m[0])` checks
must be real.  `unbounded5` remains a declaration-order case.  Next is
**M3 — open view descriptors — done (2026-10-23).**  Nested open-array
formals parse; fixed/open rank-2/3 arrays and rank-2/3 subviews are
passed as `ArrayView` pointers; open multi formals index through
`count/stride/base/next`; `HIGH`/`LEN` read the view count; `VAR` and
value open multi calls share the view (no payload copy).  Row → 1-D and
`ARRAY OF BYTE` conversions still use the legacy descriptor adapter, now
with copy-back for `VAR` and `free` after the call; migrating the 1-D
descriptor itself is M4.  Tests: `t_open2d*`, `t_open3d*`,
`t_open_row_to_1d`, `t_open_flatten_byte`; corpus **518/612**.  Next is
M4: `SIZE`/`TSIZE`/`ADR`, 1-D view migration, remaining copy cases.

## 4. Runtime range checks — done, follow-ups

`Lower.CheckSub` covers assignment, value actuals, `RETURN` and
`INC`/`DEC`; the `FOR` final increment is exempt.  Possible follow-ups:

- `LONGINT`/`CARDINAL` subranges (currently skipped);
- `FOR` control variables (decide whether to range-check the initial
  bound only, as now);
- trap tests for CHAR/enum subranges (currently integer).

## 5. Library folders / separate compilation — deferred plans

- `docs/plan-separate-compilation.md` — stable symbols, per-unit
  objects, init order, linker; and the appendix on dialect folders.
- Library-folder layout (`lib/pim`, `lib/iso`, `lib/m2r10`, shared
  `runtime/syslib`) is a low-risk build change, to do after the
  compiler language work; no need to mix dialects in one session.

## 6. Corpus leftovers (classify first)

`ptrarray3` (open-array actual), `unbounded7` (2-D actual for
`ARRAY OF BYTE`), `adraddress` (ADDRESS/pointer compare), `proc` /
`shift3` / `shift4` (decl-order), `constprocedure`/`constvec3`/
`conststrarray` (mostly ordered decls).  Park gm2 extensions, wide sets
(`settest1/3`) and `CHAR.mod` as before.

## Gates for every step

```sh
cd compiler && ./build.sh && ./run_tests.sh          # 283/283
cd .. && TMP="$PWD/.scratch/fixpoint" ./bootstrap/fixpoint.sh
tools/v3-corpus/corpus.sh                            # 512 OK, 0 crash
```

Update `STATUS.md`, `features.md`, `gaps/`, the comparison table and a
session summary; commit with a `v3-*` tag.  Do not push without asking.

## Resume

```sh
cd .../m2compiler-V3
git checkout master
cd compiler && ./build.sh && ./run_tests.sh          # 283/283
cd .. && TMP="$PWD/.scratch/fixpoint" ./bootstrap/fixpoint.sh
tools/v3-corpus/corpus.sh                            # 512 OK, 0 crash
```

**Recommendation:** take the multi-dimensional open-array ABI
decision, or start the separate-compilation/library-folder work.
`FINALLY`/module termination is now implemented.
Library folders and separate compilation remain deferred
(`docs/plan-separate-compilation.md`).