# Session 2026-10-22 — corpus triage: three conforming clusters

Branch **`master`**.  Continues `summary_session-2026-10-19.md`; the
only plan source was its "Remaining" list (corpus `LANG` triage).

## Numbers

| gate | session start | end |
| --- | --- | --- |
| suite (`compiler/run_tests.sh`) | 249/249 | **252/252** |
| fixpoint (`bootstrap/fixpoint.sh`) | OK (3,882,337 B) | **OK (3,906,044 B)** |
| corpus (`tools/v3-corpus/corpus.sh`) | 467/612 | **485/612, 0 crashes** |

Reproduce:

```sh
cd compiler && ./build.sh && ./run_tests.sh          # 252/252
cd .. && TMP="$PWD/.scratch/fixpoint" ./bootstrap/fixpoint.sh
tools/v3-corpus/corpus.sh                            # 485 OK, 0 crash
```

## Triage method

The 118 `LANG` entries were compiled one at a time (a single-file
version of `corpus.sh`), and each first diagnostic was read against its
source line.  They fall into these buckets:

| bucket | count | verdict |
| --- | --- | --- |
| imports `libc` but uses a libc function as a value (`printf`/`malloc`) | ~48 | **libc prototypes missing**; V3's permissive `FROM libc IMPORT` has no result type, so expression use is `invalid call` |
| declaration order (type/const/var used before its declaration) | ~25 | correctly rejected (`docs/gaps/`); not a target |
| gm2 extensions (`ASM`, `''` NUL char, `666B`, absolute `VAR [addr]`) | ~7 | not a target unless chosen |
| ISO features actually missing | ~20 | sized SYSTEM types (`WORD32`/`BITSET32`/qualified `SYSTEM.CARDINAL8`), `PACKEDSET`, exceptions/`UNIQUE`, `__FUNCTION__`, `PROC` as a result type |
| **conforming** clusters: arrays, subranges, ordinal `FOR`, empty string | 18 | **fixed this session** |

## What landed

### PIM/ISO multi-index arrays — `compiler/src/M2.atg`
`ARRAY [0..1], [0..2] OF T` is the standard spelling (17 corpus files
use it; none use V3's single-bracket comma list).  `ArrayType` now
parses one bracket group per dimension (`{ "," "[" ... "]" }`) and
appends every group's bounds before the element type; nesting stays
inside-out, so the layout matches `ARRAY [0..1] OF ARRAY [0..2] OF T`.
The old `ARRAY [0..1, 0..2] OF` form still works.  Corpus **+6**:
`arraybool`, `assignment2`, `foo`, `recordarray2`, `tinyarray4/5`.
Regression `t_multidim`.

### Subranges keep their ordinal base — `SymTab`, grammar
A subrange was always `FSub` with no base descriptor, so `ClassOf`
returned `ClInt` for `['A'..'Z']` and `[red..blue]`: assigning a
`CHAR`/enum literal (or comparing with one) failed.  `SymTab.NewSubB`
stores the base when both bounds have the same type; `ClassOf`,
`SubBounds`, `SetSpan`/`BaseSpanOk` and the set-span check now follow
it.  `Assignable`/`EqCheck`/`OrdCheck` accept a base value against a
subrange of the same `CHAR`/`BOOLEAN`/enum base (two different enums
stay incompatible).  Corpus **+3**: `subrange16`, `subrange17`,
`enum3`.  Regression `t_subrange`.  Assignment range checks remain
(future) — V3 is already lenient for the integer family.

### `FOR` over ordinals + typed `MIN`/`MAX` of sets — grammar
`FOR` accepted only the integer family.  It now accepts any ordinal
control variable (bounds must be assignment-compatible with it), which
covers enums and `CHAR`.  `MIN`/`MAX` of a `SET` now yields the set's
base type instead of `INTEGER`, so `FOR i := MIN(S) TO MAX(S)` binds
(the bound was previously `INTEGER` against an enum `i`).  Corpus
**+3**: `forloop2`, `smallset4`, `minmax`.

### ISO empty string literal — `SymTab` + grammar + `Lower`
ISO makes the empty string literal (`""` / `''`) length 0 and
compatible with `CHAR`, where its value is the terminator.  V3 typed it
as an ordinary string, so `ch := ""`, `ch = ""`, `CASE ch OF ""`,
`FOR ch := "" TO …`, a `CHAR` formal actual, and `RETURN ""` either
failed (`incompatible assignment`/`comparison`, `invalid Fact`) or
stored a descriptor address.

`SymTab.NewEmptyStr` marks the literal's type (`tlo = -2`); it is still
`ClStr`, so `ARRAY OF CHAR` contexts keep working (`s := ""`, `s = ""`,
`t_strempty`).  `Assignable`/`EqCheck` accept it against `CHAR`, and
`Lower` substitutes the value `0` when the context is a character
(assignment, relation, `CASE` label, `FOR` bound, value actual,
`RETURN`).  Corpus **+6**: `arraychar`, `arraychar2`, `arraychar3`,
`nulcharcase`, `nulcharvar`, `forloopnulchar`.  Regression
`t_emptychar`.

## Remaining (for a next session)

1. **`libc.def`** — the single biggest corpus bucket (~48 files).  A
   minimal definition module (`exit`, `printf`, `malloc`, `write`, …)
   needs the grammar to prefer it over the permissive `FROM libc
   IMPORT` path, plus a varargs marker for `printf`.  This is library
   work with a real payoff.
2. **ISO SYSTEM sized types** — `WORD32`/`WORD16`/`WORD8` and
   `BITSET8/16/32/64` are missing, and qualified `SYSTEM.CARDINAL8`
   does not resolve (predefs live in the global scope, not a SYSTEM
   module).  ~8 files.
3. **`PACKEDSET`**, ISO exceptions/`UNIQUE`, `__FUNCTION__` — each
   one or two files; larger or gm2-flavoured.
4. **Runtime subrange range checks** — the remaining conformance
   difference from this session's subrange work.
5. `STATUS.md` "what remains" is the live list.