63 lines
2.3 KiB
Markdown
63 lines
2.3 KiB
Markdown
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# Phase 288.1 P1: REPL Session Persistence + Auto-Display (instruction sheet)
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## Objective
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- Make REPL variables persist across input lines (`x = 1` then `print(x)` works).
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- Add minimal expression auto-display and `_` last-value binding (REPL-only).
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- Keep file mode semantics unchanged; quick smokes must remain green.
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SSOT:
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- `docs/reference/language/repl.md`
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## Constraints (non-negotiable)
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- No new env vars.
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- No file-mode behavior changes.
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- Keep REPL-specific state and logic isolated (Box-first).
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## Design (recommended)
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Do **not** persist `ValueId` across evaluations. Persist runtime values (VMValue/handle) in `ReplSessionBox`, and bridge them via a REPL-only rewrite step.
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### Bridge approach: REPL-only AST rewrite
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In REPL mode, rewrite variable reads/writes that are not declared in the current input line into calls against a REPL session object:
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- Read `x` → `__repl.get("x")`
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- Assignment `x = expr` → `__repl.set("x", expr)`
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- `_` is treated as a normal name in the session (written by auto-display).
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This keeps the parser unchanged and avoids contaminating the normal MIR builder scope model.
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### Session API (REPL-only)
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Provide a minimal host object `__repl` with:
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- `get(name: String) -> Any` (Fail-Fast if missing)
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- `set(name: String, value: Any) -> void`
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- `reset() -> void`
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Implementation options:
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- Rust VM only (initially): inject `__repl` as a built-in box/object available only in `--repl`.
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- LLVM parity is not required for Phase 288.1; REPL is a dev tool.
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## Step-by-step
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1) Add a REPL-only `__repl` host object and VM handlers for `get/set/reset`.
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2) Implement AST rewrite in the REPL runner before compilation:
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- Collect “declared names” in the current line (`local name`, function params, etc.).
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- Rewrite remaining identifier reads/writes to `__repl.get/set`.
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3) Implement auto-display:
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- If the input is a pure expression, `print(result)` (or equivalent) in REPL only.
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- Store result into session name `_` (skip if `void`).
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4) Add conformance checks (manual is OK if no test harness exists yet):
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- `x = 1` (silent)
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- `print(x)` prints `1`
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- `y` (read) is NameError
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- `1 + 1` prints `2` and `_` becomes `2`
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- `.reset` clears variables (`print(x)` errors)
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5) Run regression gate:
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- `./tools/smokes/v2/run.sh --profile quick` must stay `0 FAILED`.
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