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