# Session summary — 2026-10-08 (b): generics increment 2

Tag `v3-generics-inc2`, branch `generics-inc2` (off `generics-inc1`).
Suite **190/190**; fixpoint **OK** (**3,472,663 bytes**).

Increment 2 of ISO 10514-2 generics: a refinement now **instantiates**
the generic by re-parsing its source with the type formals bound to the
actuals — the design sketched in `docs/analysis_generics.md`.

## 1. What the syntax does now

```modula2
GENERIC DEFINITION MODULE Ident (T : TYPE);      (* the template *)
PROCEDURE Id(x : T) : T;
END Ident.

DEFINITION MODULE IntId = Ident(INTEGER);        (* a refinement *)
END IntId.
```

`IntId` is now a real module: its `Id` takes/returns `INTEGER`.  A
program `FROM IntId IMPORT Id; … Id(42)` compiles and returns 42.

## 2. How it works

Increment 1 left: grammar recognition of the four generic module
categories, formals entered as unresolved aliases (`EnterTypeParam`),
and refinements recorded (`refInst`/`refGen`/`refActual`).

Increment 2 adds the instantiation pass:

- **Grammar** (`M2.atg`): an instantiation context
  `instActive`/`instName`/`instActual[]`/`instFk`, with accessors
  (`InstBegin`/`InstAddActual`/`InstEnd`/`InInst`) and unit/refinement
  queries (`UnitNameGet`/`UnitIsGeneric`/`UnitIsDefModule`,
  `RefineSeen`/`RefineIsDef`/`RefineInst`/`RefineGen`/`RefineActual*`),
  exported via `parser.frm`.  When `instActive`, `DefUnit`/`ImplUnit`
  rename the module to `instName`, `GenericFormal` binds each formal to
  the matching actual (`EnterTypeParamBound`), and the `END` name is
  overridden.
- **SymTab**: `EnterTypeParamBound` (a formal alias whose target is the
  actual) and `Reenter` (re-enter an already-registered module scope —
  the refinement registered `X` before the re-parse).
- **Driver** (`compiler.frm`): records each generic def/impl *file*
  (module name → path) when parsed and does **not** emit the abstract
  template; on a refinement it re-opens the generic's file, sets the
  instantiation context, re-parses, and lowers the resulting unit.

## 3. Self-hosting constraints hit (and fixed)

The self-hosted compiler is stricter than gm2; three fixes were needed:

- helper procedures must be declared **before** their callers
  (`CopyNm`) — moved the accessor block below it;
- an **array element** may not be passed to a `VAR ARRAY OF CHAR`
  formal, and an **open array** may not be assigned to a fixed array —
  the registry copies element-by-element and looks up by index;
- gm2 rejects an **anonymous fixed-size array** as a formal parameter
  type — named types `GName`/`GPath` were introduced.

## 4. Test

`g_ident.def/.mod` (the generic `Ident(T)`), `g_intid.def/.mod`
(`IntId = Ident(INTEGER)`) and `g_prog.mod` (`Id(42)`).
`run_tests.sh`: `expect_run_files GenericProg 42 …` → PASS.

## 5. Scope / remaining

- Multiple formals and multiple actuals are threaded but only a single
  `T` is exercised; `const`/procedure parameters and constraints are
  increment 3.
- Instance **dedup** is not implemented (each refinement re-instantiates).
- `GENERIC CLASS`, and generics with a program module, are untouched.
- The refinement file must appear **after** the generic's file in the
  session (the registry is populated as files are parsed), and the
  generic's def must precede its impl.

## Resume

```sh
cd .../m2compiler-V3
./bootstrap/fixpoint.sh                       # FIXPOINT OK
cd compiler && ./build.sh && ./run_tests.sh   # 190/190
```

## Files

`compiler/src/M2.atg`, `compiler/src/parser.frm`,
`compiler/src/SymTab.def`/`.mod`, `compiler/src/compiler.frm`,
`compiler/tests/g_ident.*`, `g_intid.*`, `g_prog.mod`,
`compiler/run_tests.sh`, this doc.