plans: scheme-on-sx — R7RS-small port, second consumer for 3 reflective kits
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11-phase plan from parser through R7RS conformance. Explicitly maps
which reflective kits Scheme consumes:
- env.sx (Phase 2) — third consumer, no cfg needed
- evaluator.sx (Phase 7) — second consumer, unblocks extraction
- hygiene.sx (Phase 6) — second consumer, drives the deferred
scope-set / lifted-symbol work
- quoting.sx (Phase 10) — second consumer, unblocks extraction
- combiner.sx — N/A (Scheme has no fexprs)
Correction to earlier session claim: a Scheme port unlocks THREE
more reflective kits, not four. combiner.sx stays Kernel-only.
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# Scheme-on-SX: the reflective-kit second-consumer port
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The kernel-on-sx loop documented six reflective API candidates; two are now live (`env.sx`, `class-chain.sx`). Three more — `evaluator.sx`, `hygiene.sx`, `quoting.sx` — wait on a guest with operative-free lexical scope, hygienic syntax-transformer infrastructure, and quasiquote. **Scheme is exactly that guest.**
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A correct R7RS-small implementation acts as second consumer for those three kits in one stroke. It also confirms a third independent consumer for `env.sx` (after Kernel + Tcl + Smalltalk), and a candidate fourth consumer for `class-chain.sx` (Scheme's record types have parent fields — though OO is non-core in Scheme so the fit is weaker).
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## Strategic note on `combiner.sx`
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Scheme has *no fexprs*. `combiner.sx`'s applicative/operative split is Kernel-specific machinery. **Scheme is not a second consumer for `combiner.sx`** — that file stays Kernel-only until a Maru, Klisp, or CL-fexpr port arrives. The current session's earlier claim that Scheme "unlocks four more reflective kits" was over-counted; the correct number is **three**.
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## Scope decisions
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- **Target dialect:** R7RS-small. Source-only — no images, no FFI, no C extensions, no JIT.
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- **Numbers:** integers + floats. Rationals optional (defer to phase N+1). Complex out.
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- **Tail-call optimisation:** required. Implemented via the existing SX CEK machinery — call recursion in the evaluator uses iterative `cek-call` rather than host recursion.
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- **Continuations:** `call/cc` required for R7RS. Use SX's `call/cc` primitive directly.
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- **Hygienic macros:** `syntax-rules` required. `syntax-case` deferred.
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- **Char/string semantics:** Unicode codepoints; surface API matches R7RS section 6.
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- **I/O:** minimal stub (`display`, `write`, `newline`, `read`) on SX's IO surface.
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- **`define-library`:** required for module testing; implementation reuses SX's `define-library` if it's exposed, else hand-rolls a flat module registry.
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## Architecture sketch
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```
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lib/scheme/parser.sx — reader: numbers, strings, symbols, booleans,
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chars #\c, vectors #(...), dotted-pairs (a . b),
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quasi-quote sugar, datum comments #;, block
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comments #| ... |#
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lib/scheme/eval.sx — eval-expr ENV: walks AST. Symbols → env-lookup.
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Lists → look up head; if syntactic operator
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(if/lambda/define/set!/quote/quasiquote/
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let/let*/letrec/begin/cond/case/and/or/when/
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unless/do), dispatch to native handler. Else
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apply combiner (always applicative).
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ENV is `lib/guest/reflective/env.sx` directly
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— Scheme is the third consumer for env.sx with
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NO adapter cfg (canonical wire shape).
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lib/scheme/runtime.sx — Standard environment, primitives, R7RS base.
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Variadic arithmetic, list ops, string ops,
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char ops, vector ops, define-record-type,
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syntax-rules, etc.
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lib/scheme/tests/ — Standard pattern: parse, eval, lambda+closure,
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macros (syntax-rules), call/cc, define-library,
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classic programs (factorial, Y, tree-walking,
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named let, do-loop), R7RS conformance subset.
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```
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## Roadmap
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### Phase 1 — Parser
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- [ ] Reader for R7RS lexical syntax: integers, floats, strings (with escapes), symbols (extended-identifier-character set), booleans `#t`/`#f`/`#true`/`#false`, characters `#\c` `#\space` `#\newline`, vectors `#(...)`, dotted pairs `(a . b)`, quote/quasiquote/unquote/unquote-splicing sugar (same reader macros as Kernel).
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- [ ] Datum comments `#;<datum>` (skip one whole expression).
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- [ ] Block comments `#| ... |#` (nestable).
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- [ ] Tests in `lib/scheme/tests/parse.sx`.
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### Phase 2 — Evaluator + env
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- [ ] `scheme-eval EXPR ENV` — primary entry, uses `lib/guest/reflective/env.sx` directly as the canonical scope chain. **Third consumer for env.sx.**
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- [ ] Self-evaluating: numbers, booleans, strings, chars, vectors.
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- [ ] Symbol lookup → `refl-env-lookup-with`.
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- [ ] List → look up head; syntactic operators dispatch natively; otherwise applicative call with evaluated args.
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- [ ] Tests in `lib/scheme/tests/eval.sx`.
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### Phase 3 — Syntactic operators
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- [ ] `if`, `quote`, `set!`, `define` (top-level + internal).
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- [ ] `lambda` — fixed-arity, rest-arg via dot, multi-body via implicit `begin`.
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- [ ] `let`, `let*`, `letrec`, `letrec*` — including named-let.
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- [ ] `begin` — implicit + explicit.
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- [ ] `cond`, `case`, `when`, `unless`, `and`, `or`, `do`.
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- [ ] Tests for each.
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### Phase 4 — Standard environment
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- [ ] Variadic `+ - * /` and chained comparison.
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- [ ] Type predicates (R7RS `number?`, `pair?`, `null?`, `symbol?`, `string?`, `procedure?`, `vector?`, `char?`, `boolean?`).
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- [ ] List ops: `cons car cdr caar cadr ... cddddr` (or just a subset), `list length reverse append map filter fold-left fold-right for-each`.
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- [ ] String ops: `string-length string-ref substring string-append string=? string<? char->integer integer->char`.
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- [ ] Char ops: `char->integer integer->char char-alphabetic? char-numeric?` etc.
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- [ ] Vector ops: `vector make-vector vector-length vector-ref vector-set! vector->list list->vector`.
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- [ ] I/O: `display write newline read`.
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- [ ] Numerical: `abs floor ceiling round truncate min max modulo quotient remainder gcd lcm expt`.
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- [ ] Classic programs: factorial, fib, list reversal, tree map.
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### Phase 5 — call/cc + dynamic-wind
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- [ ] `call-with-current-continuation` / `call/cc`.
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- [ ] `dynamic-wind`.
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- [ ] `with-exception-handler`, `raise`, `error`.
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- [ ] Tests: escape continuations, multi-shot via call/cc (chosen via host SX `call/cc`).
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### Phase 6 — `syntax-rules` + hygiene
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- [ ] `define-syntax`, `let-syntax`, `letrec-syntax`.
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- [ ] `syntax-rules` pattern matching, ellipsis, template instantiation.
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- [ ] Hygiene: scope-set / lifted-symbol implementation. **Second consumer for `lib/guest/reflective/hygiene.sx` extraction once that kit's API surface stabilises.**
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- [ ] Tests: hygienic identifier capture, ellipsis patterns, recursive macros.
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### Phase 7 — Reflection: `eval`, `interaction-environment`, etc.
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- [ ] `eval EXPR ENV` — applicative form of the evaluator. **Second consumer for `lib/guest/reflective/evaluator.sx` extraction.**
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- [ ] `interaction-environment`, `null-environment`, `scheme-report-environment`.
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- [ ] `environment?` predicate.
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### Phase 8 — `define-library` + module hygiene
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- [ ] `define-library`, `import`, `export`.
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- [ ] `cond-expand` for feature-flag conditionals.
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- [ ] Tests: cross-library imports, identifier renaming.
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### Phase 9 — Records
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- [ ] `define-record-type` with constructor/predicate/accessors/mutators.
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- [ ] Tests: typical record idioms.
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### Phase 10 — Quasiquote runtime
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- [ ] Backquote walker with depth tracking. **Second consumer for `lib/guest/reflective/quoting.sx` extraction.**
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- [ ] Tests including nested quasiquote.
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### Phase 11 — Conformance + scoreboard
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- [ ] Curated R7RS test slice (Chibi, Larceny, or hand-picked).
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- [ ] `lib/scheme/conformance.sh` + scoreboard.
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- [ ] Drive conformance toward 100% on chosen slice.
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## Reflective kit consumption — explicit mapping
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| Kit | When it lands | How Scheme uses it |
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|-----|--------------|-------------------|
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| `lib/guest/reflective/env.sx` | Phase 2 | Direct — canonical wire shape, no cfg needed. Third consumer. |
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| `lib/guest/reflective/evaluator.sx` | Phase 7 (will trigger the extraction) | Scheme's `eval`/`interaction-environment`/`null-environment` mirror the proposed `refl-eval`/`refl-make-environment`/`refl-current-env` triple. Second consumer → extraction unblocked. |
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| `lib/guest/reflective/hygiene.sx` | Phase 6 | Scheme's hygienic `syntax-rules` is the canonical implementation of scope sets / lifted symbols. Second consumer for the deferred Shutt-style hygiene work — Scheme's hygiene goes BEYOND Kernel's by-default-static-env-extension into proper scope-set lifting. Drives the deferred research-grade kit. |
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| `lib/guest/reflective/quoting.sx` | Phase 10 | Scheme's backquote walker is structurally identical to Kernel's `knl-quasi-walk`, with depth tracking added. Second consumer → extraction unblocked. |
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| `lib/guest/reflective/combiner.sx` | NEVER (no fexprs) | Not applicable. Stays Kernel-only until a fexpr-having consumer arrives. |
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| `lib/guest/reflective/short-circuit.sx` | Possibly Phase 3 | Scheme's `and`/`or` are syntactic, not operative; could be second consumer but adapter would need to bridge "macro that short-circuits" vs "operative that short-circuits". Marginal. |
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## Ground rules
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- **Scope:** only `lib/scheme/**` and `plans/scheme-on-sx.md` and `lib/guest/reflective/**` (for extraction work). Don't edit `spec/`, `hosts/`, `shared/`, or other `lib/<lang>/` directories.
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- **Consume:** `lib/guest/lex.sx` (character predicates), `lib/guest/reflective/env.sx` (scope chain), eventually `evaluator.sx`/`hygiene.sx`/`quoting.sx` once extracted with Scheme as second consumer.
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- **Commits:** one feature per commit. Short factual messages.
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- **Tests:** every phase ends with a test file. Conformance scoreboard at the end.
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- **Branch:** `loops/scheme`. Worktree pattern (already set up at `/root/rose-ash-loops/scheme`).
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- **Substrate gaps:** filed to `sx-improvements.md`, not fixed in this loop.
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## References
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- R7RS-small: https://small.r7rs.org/attachment/r7rs.pdf
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- Chibi Scheme — a small, readable R7RS implementation.
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- Dybvig, "Three Implementation Models for Scheme" — for the hygiene story.
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- Existing kernel-on-sx code in `lib/kernel/` — much of the parser, evaluator structure, and env handling carries over near-verbatim because Kernel and Scheme share lexical scope.
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## Progress log
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_(awaiting Phase 1)_
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