# Procedure types + indirect calls (step 3)

Tag `v3-proctypes`. Main suite 109/109 (new `t_proctype`).

## What works

- **Procedure types**: `TYPE Op = PROCEDURE (a, b : INTEGER) : INTEGER;`
  and anonymous ones in declarations
  (`VAR Error : PROCEDURE (nr, line, col : INTEGER; pos : INT32);`).
- **Type-only parameter form** (GNU shorthand used by the Coco/R
  scanner frame): `PROCEDURE (INT32) : CHAR`,
  `PROCEDURE (INTEGER, INTEGER, INTEGER, INT32)`.
- **Procedure-typed variables** (module-level and local), stored as
  pointer-sized (`l`) code pointers, zero-initialised.
- **Assigning a procedure to a procedure variable**: `f := Add;`
  emits the procedure's code address (`storel $Mod_Add_N, $Mod_f`).
- **Indirect calls**: `f(40, 2)` emits `%r =w call %t(l 0, w 40, w 2)`
  (the leading `l 0` is the static link).
- **Qualified proc-typed variables**: `M2S.Error(...)`,
  `Error := Err;`.

## Implementation

- **SymTab**: new descriptor form `FProc` (result in `tref`) with
  parameters in flat arrays (`procp`/`procvis`, per-type
  `procstart`/`procn`); builder `NewProcType` + `ProcTypeAdd` +
  `SetProcTypeRes`; accessors `ProcTypeNPar/ParamType/ParamIsVar/Res`;
  `ProcTypeOf(name)` builds the type of a named procedure;
  `ClassOf` → `ClProc`; `SizeOf` 8; `Assignable` compares procedure
  types structurally (`ProcTypesOk`). Max 1024 param slots.
- **QbeGen**: `ProcAddr` (a procedure's code address as a value);
  `ClProc` handled in `DeclVar`/`AllocLocal`/`ResClass`/
  `LoadDesignator`/`ResClass`; `CallBeginInd` + `CallEnd` emit
  `call %<ptr>(...)`.
- **Grammar**: `ProcType` in `Type`; `ProcTypeSection` accepts named
  (`a, b : T`) and type-only (`T`) parameter lists; `Fact` yields a
  procedure's code address when a procedure name is used as a value
  (not followed by `(`); `ArgList`/`ActParam` gained a proc-type +
  callee path for indirect calls (used from both statement and
  expression calls).

## Limitations / follow-ups

- **Nested procedure values** are not supported: only the code
  address is stored, so the static link passed to an indirect call is
  always `0` (fine for top-level procedures). The Coco/R driver's
  `Error := StoreError` (StoreError nested in `ListHandler`) will
  need this, or a source-level restructuring.
- **Type-only parameters that are composite** (`PROCEDURE (ARRAY OF
  CHAR)`) are not parsed; only identifier type names are.

## M2S status after this step

`M2S` compiled under V3 drops from 30 errors to **3**, none
procedure-type related:

1. `M2S.mod:111` — `LENGTH(s)` (GNU builtin; V3 has `LEN`).
2. `M2S.mod:201` — empty `ELSE` in a CASE (`ELSE END`).
3. `M2S.mod:206` — `&` used for AND (in CR's *generated* scanner
   tables, not our `scanner.frm`).

These are small language-compatibility items (aliases / empty
branches), separate from procedure types.

## Files

`compiler/src/{SymTab.def,SymTab.mod,QbeGen.def,QbeGen.mod,M2.atg}`,
`compiler/tests/t_proctype.mod`, `compiler/run_tests.sh`.