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0c: persistent HAMT on Chez is ~41x faster than Janet's HAMT on the collections map-churn (258.6 -> 6.3 ms), ~15x off mutable-native (inherent persistence cost). Decision: self-host the persistent collections in Clojure; substrate is not the bottleneck. See docs/chez-phase0-results.md. 0a hardening: NUL-separated keyword intern key (no ns/name collision), non-finite -safe jolt-hash. 37/37.
48 lines
2.7 KiB
Markdown
48 lines
2.7 KiB
Markdown
# Chez port — Phase 0 results (jolt-cf1q.1)
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De-risk + contract harness. Done; all gates green. Decisions feed Phases 1–3.
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## 0a — value model (`host/chez/values.ss`, `test/chez/values-test.ss`)
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Jolt value layer on Chez: nil sentinel (distinct from `#f`/`'()`), interned
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keywords (NUL-separated intern key, no ns/name collision), ns+meta symbols,
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exactness-aware `jolt=` ((= 1 1.0) is false), and a `jolt-hash` consistent with
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it (non-finite-float safe). Chez's numeric tower IS Clojure's — ratios + bignums
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come free. **37/37 tests.**
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## 0b — host-neutral contract gate (`test/chez/`)
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The spec corpus is data, so one contract gates every host. Extracted 2655
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`[label expected actual]` cases from `test/spec/*.janet` into `corpus.edn` (valid
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as BOTH EDN and Janet data). `run-corpus.janet` drives ANY jolt binary (pluggable
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`JOLT_BIN`) at the CLI boundary, one fresh subprocess per case. Baseline vs Janet
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`build/jolt` (compile mode, the port's target mode): **2641/2655**, 14 known CLI
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divergences allowlisted (interpret-vs-compile leniency + invoke-collection-as-fn,
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several non-canonical vs JVM anyway). **The gate fails only on NEW divergences** —
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exactly what we want pointed at the Chez host in Phase 1+.
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## 0c — persistent-collection perf (`spike/chez/collections-experiment.ss`)
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The shim-vs-self-hosted decision for collections. Map-churn workload from
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`bench/collections.clj` (30000 assoc/get over 4096 keys), correct result (30000):
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| | mean | vs Janet | vs native ceiling |
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|---|--:|--:|--:|
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| Janet jolt HAMT | 258.6 ms | 1× | — |
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| Chez persistent HAMT (hand-Scheme) | 6.3 ms (opt3) | **~41×** | ~15× |
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| Chez native hashtable (mutable) | 0.43 ms | ~600× | 1× |
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**Decision: self-host the persistent collections in Clojure (jolt-core).** A
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persistent HAMT on the Chez substrate is ~41× faster than Janet's, so the
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substrate is not the bottleneck; a compiled-Clojure HAMT should land near the
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hand-Scheme one (cf. the mandelbrot finding that Chez compiles emitted code to
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the native ceiling). The ~15× gap to mutable-native is the inherent persistence
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cost (node-copy per assoc), identical in kind to JVM Clojure, and closes with
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transients/editable nodes when needed. Keep a Scheme-shim HAMT as fallback ONLY
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if Phase 2 shows the compiled-Clojure version underperforms.
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Caveats (spike scope): the experiment uses integer-key-as-hash (shallow,
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collision-free trie) and `merge-leaves` lacks real collision nodes — fine for the
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substrate-speed question; the real RT needs `jolt-hash` + collision handling.
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## Net
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Substrate speed (compute + collections), value model, and the parity gate are all
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validated and green. Phase 1 can bootstrap the real pipeline against a known,
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enforceable contract.
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