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

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

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.

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