# Session summary — 2026-10-01 (c): forward variables, result suffixes

Suite **175/175**; self-hosting fixpoint **OK** (image **2,899,706
bytes**).  Tag `v3-fwdvars-resultsfx`.

This session implemented **forward module-level variables** and
**expression result suffixes**, added several gm2/ISO library modules,
and fixed two bugs the new code exposed.

## Steps, tags and headline commits

| Step | Tag | What |
| --- | --- | --- |
| forward vars + suffixes | `v3-fwdvars-resultsfx` | this commit |

(Previous tag `v3-showcase21` remains the last committed feature step.)

## 1. Forward module-level variables

A procedure body may reference a module-level variable (scalar, array,
…) declared **further down** the module — gm2 tolerates this,
declaration-before-use does not.

- `SymTab` records each distinct name (`FwdVarRef`), resolves it at
  module end (`FwdVarResolve`), and exposes `IsFwdVar` so type checks
  are lenient while the type is unknown.
- The designator is emitted with a placeholder symbol (`$fwdN`) and the
  load/store is emitted at the default class; at module end
  `QbeGen.FwdPatchAll` rewrites the symbol and re-classes the load/store
  (`FixLoadClass`/`FixStoreClass`) over the buffered image.
- Lenient checks added to `ArithCheck`, `UnaryCheck`, `OrdCheck`,
  `EqCheck`, `Assignable`, and the pointer-compare branch in `Expr`
  (which treats an unresolved forward var as a scalar).
- `t_fwdvar.mod` exercises counters, booleans and an array declared
  after their users; exit 42.

## 2. Expression result suffixes

`F()^`, `F()[i]`, `F().field` — components applied to a function-call
result, via a new `ResultComp` production reached only when a call has
just parsed (so it stays LL(1)-clean).  A final scalar is loaded with
`ElemLoad`; aggregates stay as their descriptor address.

## 3. Library

Added: `LongIO`, `LongWholeIO`, `DynamicStrings` (core subset),
`SysStorage`, `TERMINATION`, and (earlier in the day) `ConvTypes`,
`IOConsts`, `SIOResult`, `StrIO`, `InOut`, `StdIO`, `WholeStr`,
`RealStr`, `LongStr`, `LongMath`, `STextIO`, `SWholeIO`, `SRealIO`.
`FileIO` gained `Exists`.  The shim gained `m2readline`,
`m2writeintwidth`, `m2realconv`, the `m2ds*` dynamic-string core, and
`ln`/`arctan` now wrap `log`/`atan`.

## 4. Bugs fixed

- Procedure values / `LONGINT` are 8-byte in array load/store and the
  parameter prologue (were 32-bit) — needed by `DynamicStrings` and
  the `StdIO` procedure stacks.
- The M2 driver's session file table was capped at 32 sources; raised
  to 128.
- Two self-hosting-order violations in `QbeGen.mod` (procedures used
  before declaration) and an array-element actual passed to a `VAR`
  array formal.
- `ClassOf` treats an unresolved alias as pointer-like, which is
  correct for opaque `String` but wrong for forward variables; the
  forward-variable path gives its placeholders scalar semantics and
  patches the real class at module end.

## 5. Not done (see `docs/language-report.md`)

- **Statement-context result suffixes** (`F()[i] := x`) — attempted
  twice; each restructuring of `AssOrCall` broke bare parameterless
  calls under self-hosting.  Reverted; the expression form is shipped.
- **Remaining library holes**: `ChanConsts`, `GenDevIF`,
  `DeviceTablePtr`, `StdChans`, `StreamFile`, `FIO`,
  `wrapclock`/`wraptime`/`wrapc`, `TimeString`.

## Resume

```sh
cd .../m2compiler-V3
./bootstrap/fixpoint.sh                       # FIXPOINT OK
cd compiler && ./build.sh && ./run_tests.sh   # 175/175
```

## Files

`compiler/src/{M2.atg,SymTab.def,SymTab.mod,QbeGen.def,QbeGen.mod,
FileIO.def,FileIO.mod}`, `compiler/tests/{t_fwdvar.mod}`, `stdlib/*`,
`runtime/syslib/shim.c`, `docs/language-report.md`, this doc.