# V3 step 3.6 — pointers: vars, NIL, deref, NEW/DISPOSE (done 2026-09-20)

Composites complete. Suite 64/64 (30 run — incl. 3 trap-aborts —
+ 34 reject). LL(1)-clean (only the known-benign TypeBlock warning).

## NIL as a real type (the key decision)

`NIL` was `InvalidType` piggy-backing on error suppression, which
made `p := NIL` silently emit nothing and `p = NIL` fold false.
Now `FNil`/`ClNil`/`dNil`: `NIL` assigns to pointers (210
elsewhere — `i := NIL` finally errors instead of vanishing),
compares with pointers via `ceql/cnel` (213 against the rest),
and is rejected everywhere else through existing predicates
(211/212/214/222/230 all automatic). Named `CONST X = NIL`
flows identically. No new error codes needed.

## Grammar (`M2.atg`)

- `PointerType` (`POINTER TO`, never open inside); `^` suffix with
  sfx discipline (address flows, load at use; chains compose:
  `pa^[i]`, `pr^.f`, `pp^^`); `< > <= >=` on pointers are 213.
- `NEW`/`DISPOSE` as builtin statements (no call syntax until
  step 4): plain vars via name, suffixed designators via address;
  210 on non-vars, 219 on non-pointers.
- `Design` root loads pointers (`LoadPtr`); `Assign` stores them
  (`StorePtr`); `VarDecl` accepts them (`{ l 0 }` data).
- `DISPOSE` nils afterwards — deviates from Wirth-undefined
  (testable postcondition, safer); `DISPOSE` is shallow (nested
  objects leak — documented); nil-deref is raw (no check).

## Backend (`QbeGen`, all probed first)

`LoadPtr/StorePtr`, `CmpL`, `DataLineL`, `NewHeap` (extern
`malloc`, size from descriptors) + recursive `InitHeap` (static
counts stored, nested objects allocated unrolled, members
otherwise garbage). Single-arg extern calls and store-immediates
(`storel 0, $p`) verified by probe before use.

## SymTab (additive only)

`FNil/ClNil/dNil`, `Assignable` nil→ptr rule, `EqCheck` nil rules.
`NewPtr/PtrBase` (Test2 heritage) finally wired.

## Tests

`t_pointer` → 42 (NEW/deref/alias/both NIL directions/DISPOSE/
nil-after), `t_ptrarray` → 15 (heap sizing, `^`-index chains),
`t_ptrrec` → 15 (record heap objects, `pr^.f` chains),
`t_ptrnest` → 10 (recursive heap allocation), `t_opaqueptr`
(pointer-to-opaque descriptors — the step-4 ADT hook),
`t_bad_deref`/`t_bad_new` → 219. Total 64.

Deferred: recursive `DISPOSE`, nil-deref trap, `HIGH`/`LEN`
(step 4 calls), class lowering, procedure-type calls.