# Next session — plan (from 2026-10-22 stop point)

**Branch:** `master` (tree clean at the stop point).  **Feature state:**
`v3-smallfix`.  **Gates:** suite **259/259**, fixpoint **OK
(4,028,447 bytes)**, corpus **511/612, 0 crashes**.

Read first: `docs/STATUS.md` (live state), `docs/features.md`,
`docs/gaps/README.md` (policy + reproducers), and
`docs/summary_session-2026-10-22.md` (what the last session did).

## Policy reminder

V3 follows **PIM/ISO Modula-2**, not gm2's leniencies.  Declaration
before use is required for data; the only forward type reference is a
`POINTER`'s base.  gm2 compatibility is accepted only where explicitly
chosen and documented (`docs/gaps/README.md`).  The corpus is gm2's
testsuite, so `LANG` includes deliberate rejections; classify before
fixing.

## 1. `PACKEDSET` — 3 corpus files (`onebyte`, `onebyte2`, `onebyte3`)

ISO 10514-1 has `PACKEDSET OF <ordinal>`; XDS states that the standard
does not mandate a representation and treats sets/packedsets the same.
Options:

- **Minimal:** parse `PACKEDSET` as `SET` (the XDS interpretation) and
  document that the representation is not bit-packed.  This compiles the
  three files but `onebyte*` may test `SIZE`/bit layout — inspect first.
- **Faithful:** add a packed representation (1/2/4-byte masks), which
  means new set ops at byte granularity in `QbeGen` and type sizing.

Suggested decision: inspect `onebyte*`; if they only use set operations
(not `SIZE`-sensitive), map to `SET` and document.  Add a regression.

## 2. ISO exceptions — 7 corpus files (`except2/4/5/7/8/9`, `lazyunique`)

This is a **feature**, not a parser tweak:

- `EXCEPT` / `RETRY` after a normal statement sequence (procedures and
  module bodies);
- `EXCEPTIONS` (AllocateSource/RAISE/CurrentNumber/GetMessage/
  IsCurrentSource/IsExceptionalExecution) and `M2EXCEPTION`;
- runtime support (handler stack / `setjmp`-`longjmp` or equivalent);
- `lazyunique` also needs ISO `UNIQUE` module support.

Design a minimal handler model first (one active handler per procedure,
exception state per coroutine, re-raise on unhandled), then implement.
Budget a dedicated session; do not start it as a "small fix".

## 3. Multi-dimensional open arrays — 8 corpus files

`unbounded`, `unbounded2/3/4/6/8`, `array9`, `adrunbounded3`.
**Do not just accept them**: V3 represents each array level as its own
descriptor, while gm2 passes a flat block with strides.  The corpus
files check `ADR(m) = ADR(m[0]) = ADR(m[0][0])` and flat `SIZE` values,
so compiling them would silently miscompile.

Next step is an **ABI decision**:

- keep the nested-descriptor model and add a flat/strided open-array
  descriptor for multi-dimensional formals (real work), or
- document the limitation and leave this bucket parked.

`unbounded5` is different: a type declared after its use (decl-order
gap), not this feature.

## 4. Runtime subrange range checks — conformance

V3 accepts base-typed values into CHAR/enum subranges (2026-10-22) but
emits no runtime range check, and is already lenient for the integer
family.  Add `QbeGen.CheckRange` on assignment / parameter binding /
`RETURN` where the destination is a subrange, with an `abort` trap; add
trap tests (like `t_trap_index`).  This is the main remaining
conformance difference from the subrange work.

## 5. Optional / larger

- **ISO 10514-3 OO** vs the Clarion-form `CLASS`.  Large; only if OO
  conformance becomes a goal.
- **A real `stdlib/libc.def`** instead of the built-in prototype table.
  Not needed for the corpus; useful for user code (`DEFINITION MODULE
  FOR "C"`, varargs, `SYSTEM.CSIZE_T`).
- **Small corpus leftovers** (classify first): `ptrarray3` (open-array
  actual), `unbounded7` (2-D actual for `ARRAY OF BYTE`), `adraddress`
  (ADDRESS/pointer compare), `proc` (decl-order), `shift3/4`
  (decl-order), `constprocedure`/`constvec3`/`conststrarray` (mostly
  ordered decls).

## Known non-targets / parked

- gm2 extensions: `ASM`, address arithmetic, absolute `VAR [addr]`,
  `666B`/`012H` literals, `SHORTREAL` as 32-bit, char arithmetic,
  set ordering (`largeset5`), module named `CHAR`.
- decl-order cases (gaps 01–06, 19–21) — V3 rejects them by policy.
- wide sets (`settest1/3`): implementation limit (span > 65536).
- `CHAR.mod`: a module named `CHAR` collides with the pervasive type.

## Gates for every step

```sh
cd compiler && ./build.sh && ./run_tests.sh          # must stay 100%
cd .. && TMP="$PWD/.scratch/fixpoint" ./bootstrap/fixpoint.sh
tools/v3-corpus/corpus.sh                            # record OK/CRASH
```

Then update `docs/STATUS.md`, `docs/features.md`, `docs/gaps/` and the
comparison table, and commit with a `v3-*` tag.  Do not push without
asking; tags are immutable per feature.

## Resume

```sh
cd .../m2compiler-V3
git checkout master
cd compiler && ./build.sh && ./run_tests.sh          # 259/259
cd .. && TMP="$PWD/.scratch/fixpoint" ./bootstrap/fixpoint.sh
tools/v3-corpus/corpus.sh                            # 511 OK, 0 crash
```

**Recommendation:** start with `PACKEDSET` (after inspecting
`onebyte*`), then the subrange range checks; reserve a whole session for
ISO exceptions, and make an explicit ABI decision before touching
multi-dimensional open arrays.