# V3 step 4.1 — procedure calls: emission, frames, recursion (done 2026-09-22)

Suite 79/79 (37 run — incl. 4 trap-aborts — + 42 reject).
LL(1)-clean (only the known-benign TypeBlock advisory).
Module-level procedures only; nested lowering = 4.2.

## What lowers now

- **Calls as expressions and statements**: value params (with
  `INTEGER`→`REAL` conversion), `VAR` params by address,
  function results, recursion, mutual recursion through
  `FORWARD`, open-array `VAR` formals over fixed actuals,
  string literals into open `CHAR` formals. Arity/type
  failures are 233 (`invalid call`, new message); proper-as-
  function and function-as-statement are 233; composite
  results stay 230; open *value* formals are 230.
- **Frames**: value params copied to slots on entry (scalars,
  pointers, sets, arrays via `CopyArray`, records via
  `CopyRecord`); `VAR` params stay addresses; locals in stack
  slots (`alloc4/8`); named consts get function-mangled data.
  Same-named methods mangle by proc uid (`$Init_3`).
- **Bodies**: `RETURN` emits (`ret`, converted when widening);
  fall-off-end gets a typed default; `FORWARD` headings emit
  nothing (buffered header discarded).

## Backend lessons (all probed, not guessed)

- QBE accepts statement-calls, 8-arg spill, `l` params,
  recursion, and forward references (all proven before use).
- **Reentrancy**: nested calls (`Acc(t, Double(5))`) clobbered
  the shared call state (wrong target + merged args). Fixed
  with a 16-deep call stack; 64-arg/level cap → 233.
- **Zero-init locals**: the frontend's dead target-load (Test2
  heritage, harmless for globals) reads never-stored stack
  slots, which QBE rejects. Scalar/pointer/set slots now
  zero at alloc — consistent with the zero-initialized
  globals (arrays/records need no loads: `AddrOf` only).
- Single-letter SSA temps mislink (3.1 rule, re-observed).

## SymTab (additive)

`ProcUid` (mangled names), `ProcNPar`/`ParamType`/`ParamIsVar`
(call checking), `ProcDepth` (nesting detection), `VarParamOk`
(same type, fixed→open, literal→open-CHAR). `NIL` (`FNil`,
3.6) needed zero changes — `p := NIL`, `p = NIL` and the 233s
all worked through the new paths untouched.

## Grammar notes

- `NIL` exempted from the named-const 230 (else nothing with
  `NIL` compiles); bare proc names shed their eager 230 (the
  following `ArgList` decides; `Fact` reports 230 when none).
- `AssOrCall` merges assignment and statement calls (`:=`
  vs `(` are LL(1)-distinct); bare `P;` is now a syntax error
  (was silently accepted — strictly better).
- VAR actuals resolve through a temp→address note table
  (ring of 256; exact because SSA temps never repeat), so no
  expression-rule signatures changed. WITH-field actuals work
  (un-deferring the step-3 note).
- `F()^` result suffixes are still syntax errors (deferred).

## Tests

`t_call` → 125 (results, recursion), `t_varpar` → 40 (swap,
address semantics), `t_mutual` → 11, `t_withfield` → 13,
`t_valarray` → 6 (copy proven: aliasing would give 104),
`t_openarr` → 7, `t_nestedproc` → 230; `t_proc`/`t_forward`
promoted to run (0); `t_bad_arity`/`t_bad_actual`/
`t_bad_funstmt` → 233; `showcase9` → 140. Total 79.

Deferred: nested/display (4.2), separate compilation +
opaque completion + `HIGH`/`LEN` (4.3), proc-type vars,
`F()^` suffixes, >64 params, recursive `DISPOSE`.