prometeu-runtime/files/TODOs.md

PR-6.3 — CALL_CLOSURE (Model B Hidden Arg0)

Briefing

Closures must be dynamically invokable.

Under Model B, invocation semantics are:

• The closure object itself becomes hidden arg0.
• User-supplied arguments become arg1..argN.
• Captures remain inside the closure and are accessed explicitly.

---

Target

Introduce opcode:

CALL_CLOSURE arg_count

Stack before call:

[..., argN, ..., arg1, closure_ref]

Execution steps:

1. Pop closure_ref.
2. Validate object is ObjectKind::Closure.
3. Pop arg_count arguments.
4. Read fn_id from closure object.
5. Create new call frame:

• Inject closure_ref as arg0.
• Append user arguments as arg1..argN.

6. Jump to function entry.

No environment copying into locals.

---

Work Items

1. Add CALL_CLOSURE opcode.
2. Implement dispatch logic.
3. Integrate with call frame creation.
4. Ensure stack discipline is preserved.

---

Acceptance Checklist

• CALL_CLOSURE implemented.
• closure_ref validated.
• arg_count respected.
• Hidden arg0 injected correctly.
• Errors thrown on non-closure call.

---

Tests

1. Closure returning constant.
2. Closure capturing value and using it.
3. Calling non-closure results in trap.
4. Nested closure calls work.

---

Junie Instructions

You MAY:

• Modify interpreter call logic.
• Add tests.

You MUST NOT:

• Change stack model.
• Introduce coroutine semantics.
• Modify GC.

If function signature metadata is insufficient to validate arg_count, STOP and ask.

---

Definition of Done

Closures can be dynamically invoked with hidden arg0 semantics.

---

PR-6.4 — GC Traversal for Closures (Model B)

Briefing

Closures introduce heap-to-heap references through their captured environments.

Under Model B, the closure object itself is passed at call time, but its environment remains stored in heap.

GC must traverse:

closure -> env -> inner HeapRefs

---

Target

Extend GC mark phase to handle ObjectKind::Closure:

When marking a closure:

• Iterate over env values.
• If a value contains HeapRef → mark referenced object.

No compaction. No relocation.

---

Work Items

1. Extend mark traversal switch.
2. Ensure safe iteration over env payload.
3. Add regression tests.

---

Acceptance Checklist

• Closure env scanned.
• Nested closures retained.
• No regression in existing GC tests.

---

Tests

1. Closure capturing another closure.
2. Closure capturing heap object.
3. Unreferenced closure collected.

---

Junie Instructions

You MAY:

• Modify mark traversal.
• Add tests.

You MUST NOT:

• Modify sweep policy.
• Introduce compaction.

If unsure whether Value variants can embed HeapRef, STOP and ask.

---

Definition of Done

GC correctly traverses closure environments under Model B semantics.

---

PR-6.5 — Verifier Support for Closures (Model B)

Briefing

The verifier must understand closure values and enforce safe invocation rules.

Under Model B:

• CALL_CLOSURE injects hidden arg0.
• User-visible arg_count excludes hidden arg.
• Captures are accessed via explicit instructions (future PR).

---

Target

Extend verifier to:

1. Introduce stack type: ClosureValue.
2. Validate MAKE_CLOSURE effects.
3. Validate CALL_CLOSURE semantics:

• Ensure top of stack is ClosureValue.
• Ensure sufficient args present.
• Validate arg_count matches function signature expectations.
• Account for hidden arg0 when checking callee arg arity.

4. Validate ret_slots against function metadata.

---

Work Items

1. Extend type lattice with ClosureValue.
2. Define stack transitions for MAKE_CLOSURE.
3. Define stack transitions for CALL_CLOSURE.
4. Enforce strict failure on mismatch.

---

Acceptance Checklist

• ClosureValue type exists.
• Invalid CALL_CLOSURE rejected.
• Hidden arg0 accounted for.
• ret_slots validated.
• All verifier tests pass.

---

Tests

1. Valid closure call passes verification.
2. CALL_CLOSURE with wrong arg_count fails.
3. CALL_CLOSURE on non-closure fails verification.
4. Nested closure calls verify correctly.

---

Junie Instructions

You MAY:

• Extend verifier model.
• Add tests.

You MUST NOT:

• Weaken verification rules.
• Replace verifier checks with runtime-only traps.

If function metadata (arg_slots/ret_slots) is insufficient, STOP and request clarification.

---

Definition of Done

Verifier fully supports closure creation and invocation under Model B semantics.