# Session summary — 2026-09-30: aggregate constructors + showcase20

Suite **159/159**; self-hosting fixpoint **OK**
(image **2,639,067 bytes**). `master`, tree clean except the user's
uncommitted `compiler/toto.mod`.

This session added GNU Modula-2 **aggregate constructors** and
showcased them.

## Steps, tags and headline commits

| Step | Tag | Commit | What |
| --- | --- | --- | --- |
| Array constructors | `v3-array-ctors` | `c03563e` | `T{…}` static descriptors |
| Records + runtime | `v3-ctor-records` | `382125a` | `Rec{…}`, runtime build |
| Showcase | `v3-showcase20` | (this commit) | constructors end to end |

## 1. Constructors

`TypeName{…}` (GNU Modula-2) is now an aggregate constructor for arrays
and records:

- **Static** — when every element is a constant, `CtorEnd` bakes a
  pooled descriptor (`data $ctoN = { … }`) with the same layout as a
  declared object: array `l n, …`, record fields in declaration order,
  nested constructors inlined as aggregate fields (and consumed),
  strings inlined into matching `CHAR`-array fields.  A `CONST` of an
  aggregate type resolves to the descriptor address.
- **Runtime** — any non-constant element makes `CtorEnd` allocate the
  descriptor on the stack (`alloc8`) and fill it in place
  (`ElemStore` / `InitArrHeader`+`CopyArray` / `CopyRecord` /
  `CopySet`), so constructors also work outside `CONST`.
- Elements: scalars, nested constructors, strings for `ARRAY OF CHAR`,
  and the `expr BY n` repeat form.

`QbeGen.CtorBegin/CtorElem/CtorEnd` (`CtorElem` derives the element
type itself); the old `TypedSetLit` became the unified `TypedBraceLit`
(`BITSET{…}` stays a set).

## 2. Showcase

`compiler/tests/showcase20.mod` (`Showcase20`, exit 42) exercises:

- `Greet = Name {'H','e','l','l','o','!','!','!'}` — CHAR-array CONST;
- `Base = Triple {7, 7 BY 2}` — the `BY` repeat form (7,7,7);
- `p := Person{"Modula", Date{1980, 5, 3}}` — static record
  constructor (string field + inlined nested record);
- `q := Person{"Runtime", Date{i, i+1, i+2}}` — runtime record
  constructor;
- `a := Triple{i, i+1, i+2}` — runtime array constructor.

Sum: `21 (Base) + 18 (a) + 3 (p.born.d) = 42`.

```
showcase20 total=42
```

## Tests (159, was 155)

New: `Showcase20` (42), plus `t_ctor{1..6}` (`t_ctor1` CHAR-array
copy, `t_ctor2` `BY` repeat, `t_ctor3` nested strings, `t_ctor4`
static record, `t_ctor5` runtime array, `t_ctor6` runtime record).

## Corpus (with `$V3_LIBS`)

gm2 testsuite **283/612** compile-OK (was 242 before this work; 0
CRASH).  `strcons.mod`, `testarray.mod`, `arrayconst{1,2,3}.mod`,
`lazyunique.mod`'s array constructor now compile.

## Resume

```sh
cd .../m2compiler-V3
./bootstrap/fixpoint.sh                       # FIXPOINT OK
cd compiler && ./build.sh && ./run_tests.sh   # 159/159
```

## Remaining

- Set fields in record constructors; constant string concatenation in
  constructor elements.
- `ARRAY <type> OF T` (index-type arrays).
- `MIN`/`MAX` builtins; more `SYSTEM` facilities.