124 lines
4.5 KiB
Markdown
124 lines
4.5 KiB
Markdown
# PBS IR and Lowering Agenda
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Status: Active
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## Purpose
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Drive the decisions needed to turn `12. IR and Lowering Specification.md` from a skeleton into a normative lowering contract that can guide implementation.
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## Context
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The language now has substantial source-level semantics, but lowering still lacks closure around:
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- which semantic obligations IR must preserve,
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- whether one canonical IR shape is normative,
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- how core constructs map into lowered control flow and data flow,
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- how services, contracts, callbacks, tuples, `optional`, and `result` lower,
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- and which invariants belong in lowering versus PBX/bytecode mapping.
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This agenda should keep the focus on semantic preservation and artifact obligations, not on one compiler's class hierarchy.
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## Decisions To Produce
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1. Decide the normative status of IR:
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canonical IR, canonical obligations only, or hybrid.
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2. Decide the required lowering preconditions after parsing, resolution, and type checking.
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3. Decide the lowered forms required for expressions, control flow, abrupt completion, and propagation.
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4. Decide the lowering story for callbacks, services, contracts, tuples, `optional`, and `result`.
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5. Decide the boundary between this spec and `15. Bytecode and PBX Mapping Specification.md`.
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6. Decide the artifact invariants that must hold before verifier or loader stages.
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## Core Questions
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1. Which evaluation-order guarantees from dynamic semantics must be explicit in lowered form?
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2. Which memory and identity facts must remain explicit through IR rather than inferred later?
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3. Do callback formation and contract dispatch need dedicated runtime artifacts or only preserved semantic obligations?
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4. What is the minimal lowering model for builtin projections, builtin constants, and intrinsic member calls beyond what is already fixed?
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5. Which host-binding failures are lowering failures versus later verifier or loader failures?
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## Proposed Workshop Sequence
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### Workshop 1: Lowering Contract and IR Status
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Purpose:
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- decide whether PBS standardizes one canonical IR or only preserved obligations,
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- and close lowering preconditions after parsing, resolution, and type checking.
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Expected decisions:
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- canonical IR versus obligations-only model,
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- required bound-program inputs,
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- and minimal preserved semantic facts.
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### Workshop 2: Control Flow, Evaluation Order, and Propagation
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Purpose:
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- close the lowering model for expressions, branching, abrupt completion, `optional`, and `result`.
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Expected decisions:
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- explicit evaluation-order preservation,
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- lowered forms for `else`, `!`, and `handle`,
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- and trap versus propagation boundaries.
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### Workshop 3: Callables, Services, Contracts, and Callbacks
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Purpose:
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- close the lowering story for callable categories beyond ordinary top-level functions.
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Expected decisions:
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- callback formation model,
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- service and contract dispatch shape,
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- and runtime-artifact obligations for callable categories.
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### Workshop 4: Builtins, Host Bindings, and Artifact Invariants
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Purpose:
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- close builtin lowering, host-binding emission, and the invariants required before verifier and loader stages.
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Expected decisions:
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- builtin projection and intrinsic lowering obligations,
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- host-binding emission boundary versus PBX mapping,
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- and artifact invariants consumed by `15` and `19`.
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## Expected Spec Material
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The resulting spec work should be able to add or close sections for:
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- lowering preconditions,
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- preserved semantic obligations,
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- control-flow lowering,
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- callable lowering by category,
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- tuple, `optional`, and `result` lowering,
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- callback, service, and contract lowering,
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- builtin and host-binding lowering,
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- artifact invariants before PBX emission,
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- and source-to-artifact trace hooks consumed by diagnostics and conformance.
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## Non-Goals
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- Freezing optimizer internals.
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- Freezing one in-memory compiler IR data model.
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- Repeating the bytecode ISA.
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- Defining loader patching internals.
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- Designing performance heuristics.
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## Inputs
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- `docs/pbs/specs/4. Static Semantics Specification.md`
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- `docs/pbs/specs/6. VM-owned vs Host-backed.md`
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- `docs/pbs/specs/6.1. Intrinsics and Builtin Types Specification.md`
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- `docs/pbs/specs/6.2. Host ABI Binding and Loader Resolution Specification.md`
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- `docs/pbs/specs/9. Dynamic Semantics Specification.md`
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- `docs/pbs/specs/10. Memory and Lifetime Specification.md`
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- `docs/pbs/specs/12. IR and Lowering Specification.md`
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- `docs/pbs/specs/14. Name Resolution and Module Linking Specification.md`
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- `docs/pbs/specs/15. Bytecode and PBX Mapping Specification.md`
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- `docs/pbs/specs/16. Runtime Execution and Initialization Specification.md`
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