prometeu-studio/docs/pbs/agendas/12.1. IR and Lowering Workshop 1 - Lowering Contract and IR Status.md

PBS IR and Lowering Workshop 1

Status: Active

Purpose

Run the first focused discussion for 12. IR and Lowering Specification.md on the front door of lowering:

• what the lowering contract consumes,
• whether IR itself is normative,
• and which semantic obligations must be preserved independent of IR shape.

Why This Slice First

This slice should come first because every later lowering discussion depends on knowing:

• what counts as a well-formed input to lowering,
• and whether the spec standardizes one IR shape or only semantic preservation duties.

Proposed Meeting Order

1. Reconfirm already-settled lowering inputs.
2. Close the preconditions for lowering.
3. Close the normative status of IR.
4. Close the minimum preserved semantic obligations.
5. Record construct-specific issues for later workshops.

Decisions To Produce

1. The normative status of IR in PBS v1.
2. The minimum required input state before lowering begins.
3. The semantic facts that lowering must preserve regardless of IR architecture.
4. The boundary between 12 and 15.

Candidate Decisions

1. Standardize Preserved Obligations, Not One Canonical In-Memory IR

Candidate direction:

• PBS v1 does not require one canonical compiler IR data model,
• but it does require one stable set of preserved semantic obligations.

Rationale:

• This keeps the spec implementation-neutral while still preventing semantic drift.

Alternative to discuss:

• define one normative abstract IR grammar in the spec.

2. Lowering Preconditions Require A Fully Bound Program

Candidate direction:

• parsing, name resolution, visibility/linking, and type checking must already be complete,
• reserved builtin and host metadata must already be validated,
• callable sets and canonical identities must already be resolved.

Rationale:

• Lowering should not invent unresolved semantic answers.

3. Minimum Preserved Obligations Include Evaluation Order, Identity, and Host Boundary Facts

Candidate direction:

• lowering must preserve: source-observable evaluation order, abrupt-completion behavior, value-identity and aliasing facts, host-boundary crossings, and trap-versus-propagation distinctions.

Rationale:

• These are the semantic anchors later workshops will rely on.

4. 15 Owns Final Artifact Layout, 12 Owns The Contract Before It

Candidate direction:

• 12 defines the semantic and artifact-facing invariants a lowered program must satisfy,
• 15 defines the final PBX and bytecode mapping details.

Rationale:

• This keeps the lowering spec from collapsing into artifact byte layout.

Questions To Resolve In The Room

1. Is obligations-only precise enough, or does PBS need a normative abstract IR?
2. Should canonical identity resolution be fully complete before lowering?
3. Which semantic facts are mandatory to preserve explicitly rather than infer later?
4. Does 12 need one explicit “bound program” model?
5. How much artifact vocabulary can 12 use before it starts stealing 15's job?

Expected Outputs

1. a decision record on IR status,
2. a decision record on lowering preconditions,
3. and a checklist of preserved semantic obligations for 12.

Explicit Deferrals For Workshop 2

• control-flow shapes,
• propagation operators,
• and callable-category-specific lowering.

Inputs

• docs/pbs/specs/9. Dynamic Semantics Specification.md
• docs/pbs/specs/10. Memory and Lifetime Specification.md
• docs/pbs/specs/12. IR and Lowering Specification.md
• docs/pbs/specs/15. Bytecode and PBX Mapping Specification.md
• docs/pbs/agendas/12. IR and Lowering Agenda.md