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Documents the extraction (Smalltalk + CLOS migrated, kit landed, counts unchanged), lists plausible third consumers (JS proto chain, Ruby ancestors, Python MRO), and notes which other patterns stayed unextracted and why (method-cache invalidation, inline cache, and the five reflective siblings all need consumers that don't exist yet in the codebase). Closes the session's extraction work at five branches: env (3 consumers), class-chain (2), test-runner (POC), plus the chain of intermediate branches. The Scheme port is the next high-leverage move; it would unlock four more reflective kits in one stroke.
60 lines
3.9 KiB
Markdown
60 lines
3.9 KiB
Markdown
# lib/guest/reflective/class-chain.sx — extraction plan
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## Status
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- [x] **Kit landed** — `lib/guest/reflective/class-chain.sx` (7 forms, ~120 LoC).
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- [x] **First consumer migrated** — `lib/smalltalk/runtime.sx` `st-method-lookup-walk`. 20 lines → 9 lines. Smalltalk single-parent shape adapted via `:parents-of` returning a 1-element list.
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- [x] **Second consumer migrated** — `lib/common-lisp/clos.sx` `clos-specificity`. 28 lines → 4 lines. CLOS multi-parent shape adapted via `:parents-of` returning the full parents list.
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- [x] Both consumers' test counts unchanged. Smalltalk 847/847. CL 222/240 (18 pre-existing failures unrelated to CLOS dispatch).
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## API surface
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```lisp
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(refl-class-chain-find-with CFG CLASS-NAME PROBE)
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;; DFS through parent chain. Returns first non-nil probe result.
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;; Smalltalk method lookup uses this.
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(refl-class-chain-depth-with CFG CLASS-NAME ANCESTOR-NAME)
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;; Minimum hop count via any parent path. nil if unreachable.
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;; CLOS method specificity uses this.
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(refl-class-chain-ancestors-with CFG CLASS-NAME)
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;; Flat DFS-ordered list of all reachable ancestor names.
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```
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**Adapter cfg keys:**
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- `:parents-of` — fn (class-name) → list of parent class names. Empty list = root. Single-parent guests wrap into a 1-element list.
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- `:class?` — predicate; short-circuits walk on non-existent class names.
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## Why two consumers were enough
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Smalltalk and CLOS have *structurally different* class hierarchies — single inheritance with one `:superclass` field versus multiple inheritance with a `:parents` list. The kit handles both via the cfg normalising `:parents-of` to "list of parent names" (empty, singleton, or multi-element). This is the third demonstration of the adapter-cfg pattern from `lib/guest/match.sx` and `lib/guest/reflective/env.sx`.
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## Future consumers
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A third consumer would validate the kit further but isn't blocked by the two-consumer rule. Plausible candidates that already have class chains in the codebase or could acquire them:
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- **JavaScript prototype chains** — if `lib/js/` builds an evaluator that walks `__proto__`. `:parents-of` returns a 1-element list (the proto, if any). Probably the cleanest third consumer.
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- **Ruby's ancestor walk** (`Module#ancestors`) — multi-element list with strict ordering rules. Would stress whether `:parents-of` needs to return ordered lists (it already does).
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- **Python's MRO** (method resolution order via C3 linearisation) — could use `refl-class-chain-ancestors-with` as a starting point, with consumer-side linearisation on top.
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## Non-goals
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- **Method-cache invalidation protocol** — Smalltalk has `st-method-cache` with class-change invalidation; CLOS has per-generic method lists with `clos-defmethod` updates. Currently only one consumer per cache shape; defer.
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- **Inline call-site caches** — Smalltalk's per-call-site IC is a hot-path optimisation. No other current consumer; defer until at least a JS or Python guest with optimisable dispatch.
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- **`combiner.sx`, `evaluator.sx`, `hygiene.sx`, `quoting.sx`, `short-circuit.sx`** — these still wait for a Scheme/Maru port. CLOS doesn't have fexprs, so it can't be the second consumer for `combiner.sx`. CL's reader has backquote parsing but no runtime quasi-walker, so it's not a current second consumer for `quoting.sx` either. The Scheme port is the unlock.
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## Cumulative session output
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| Branch | Kit | Consumers |
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|---|---|---|
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| `loops/kernel` | (proposal docs) | 1 |
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| `lib/tcl/uplevel` | `reflective/env.sx` | 2 (Kernel, Tcl) |
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| `lib/smalltalk/refl-env` | `+ refl-env-find-frame-with` | 3 (+ Smalltalk) |
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| `lib/guest/test-runner` | `test-runner.sx` | 1 (Kernel POC) |
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| `lib/guest/method-chain` | `reflective/class-chain.sx` | 2 (Smalltalk, CLOS) |
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**Two complete reflective kits live with multiple consumers**; one infrastructure kit at proof-of-concept; one extraction (the Scheme port that would unlock four more reflective kits) is the next natural strategic move but is a substantial undertaking.
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