# Goals — steps 8+ (saved, to implement next)

Roadmap after step 7 (backend listing). Order is priority order;
each step keeps the full suite green with no cascades.

## Step 8 — opaque types (recommended next)

Scope (finishes the step-5 library story: information hiding):
- `TYPE T;` (opaque declaration) in `DEFINITION`; the full
  declaration in `IMPLEMENTATION` (`TYPE T = RECORD ... END;`).
- Outside the implementation, opaque `T` is usable only behind
  `POINTER TO T`, as a `VAR` formal type, and for assignment
  between same-opaques. No client `VAR` of type `T`, no field
  access, no construction, no value parameters or function
  results of opaque type (all static 230s/201s).

Design deltas (vs step 7):
- SymTab: opaque descriptor form (or alias-with-hidden-target +
  flag); export table carries opaque-ness; completion in the
  implementation reuses one descriptor index so both sides agree;
  compatibility: same-opaque assigns, nothing else crosses.
- Grammar: `TYPE` ident `;` alternative in definitions (mid-rule:
  `TYPE T = ...` stays); implementation `TYPE` accepts the
  completion (name/type match, else 221-ish/230).
- MGen: expected unchanged (clients can never size an opaque —
  pointers are 1 slot; the implementation walks the completed
  descriptor normally).

Acceptance (same bar):
- ~4 run tests (counter/stack ADT: New/Free/Use/Count ExitCodes)
  + ~5 rejection tests (client VAR, field access, value param,
  opaque result, completion mismatch); 65-test regression green.

Suggested first tests:
- `DCounter`-style ADT (`New` returns pointer, `Inc`/`Get`),
  completion mismatch (different base → reject), client
  `VAR x : T` → reject, `p^.field` from client → reject.

## Step 9 — procedure types + indirect calls

Scope: `TYPE H = PROCEDURE (INTEGER): INTEGER;` variables,
procedure constants as values, calls through variables, handlers
as actuals. Requires a VM design spike first: no direct indirect-
call opcode exists (`CE jump_stack` = bare computed jump; return
linkage/frames must be designed, possibly a new opcode or a
linkage convention in MGen). Do NOT start emitting before the
spike lands in `mc64-spec.md`.

## Step 10 — LONGINT / LONGREAL

Scope: 64-bit `LONGINT`/`LONGCARD` (`0C5–CC`), `LONGREAL` quads
(`0x12`), literals, conversions, full operator lowering, print
helper extension. Large but mechanical: lexer, descriptors, every
operator family, mixed-type rules. (Predefs currently alias to
32-bit/64-bit-float as placeholders.)

## Later (explicitly deferred)

- Multi-`.MC4` emission with `depCount` loading (loader path is
  proven by `STAK`/`DEP`; the emitter side is the work).
- Source-line mapping for `DumpImage` (needs positions on AST
  nodes: grammar + AST + backend change).
- `WITH`-field / `CHAR` tails as `VAR` actuals, open-to-open
  array passing, circular imports (v1 hardening list, unchecked
  here so far).