e66a91750e
Arithmetic and comparisons lowered to raw Chez ops, so an operand outside Chez's tower (BigDecimal) crashed with a raw condition, and Chez contagion leaked: (* 1.0 0) gave exact 0 where the JVM gives 0.0, (* ##Inf 0) gave 0 instead of ##NaN, (/ 1 0) raised an untyped error. One seam now (host/chez/seq.ss): call position emits jolt-n* macros with the both-Chez-numbers fast path open-coded; value position folds through the same binary ops. Anything outside the tower falls to per-op slow hooks that java/bigdec.ss extends, so bigdec arithmetic works in every position (the old static-only :bigdec typing limitation is gone). JVM rules patched into the fast path: a double operand wins, an exact zero divisor throws ArithmeticException while a double zero divisor yields Inf/NaN, quot/rem/mod cover ratios and doubles, min/max return the original operand with NaN winning, a nil operand is NPE and a non-number CCE, zero-arg -// throw ArityException at runtime instead of failing expansion. Also: with-precision now binds *math-context* and bigdec results round with real RoundingMode semantics (UNNECESSARY throws; division rounds to precision instead of throwing); rationalize goes through the shortest decimal print like BigDecimal.valueOf (the identity stub is gone); ratios coerce to bigdec like Numbers.toBigDecimal; min/max int-literal operands no longer coerce to flonum in the numeric pass. Perf neutral: fib and seq benches unchanged (the fast path is two type checks the optimizer folds); hinted fl/fx paths untouched. 19 JVM-certified corpus rows; cts baseline 5614->5730 pass, 192->88 errors, 84->79 baselined namespaces.
194 lines
11 KiB
Markdown
194 lines
11 KiB
Markdown
# The jolt conformance spec
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This directory defines jolt's behavior as a **host-neutral, executable language
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specification**: a data file of cases, certified against reference Clojure, with a
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feature profile that lets any runtime declare a conformance *level*. The goal is to
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make hosting jolt on a new runtime (and proving it correct) a mechanical exercise:
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read one data file, run each case, compare, report.
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## The artifacts
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| File | Role | Generated by |
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|------|------|--------------|
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| `test/chez/corpus.edn` | **The spec.** ~2900 cases of `{:suite :label :expected :actual}`, `:expected` **sourced from reference JVM Clojure**. | `test/conformance/regen-corpus.clj` |
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| `test/conformance/profile.edn` | Per-case **feature classification** — which non-portable cases need which host capability. | `certify.clj --profile` |
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| `test/conformance/known-divergences.edn` | The few rows whose JVM value is an opaque host object that can't round-trip to readable source (Java arrays/transients/atoms/beans/proxies print as `#object[..@addr]`), so the corpus keeps jolt's value. | `regen-corpus.clj` leftovers, hand-checked |
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| `test/conformance/regen-corpus.clj` | Sources every `:expected` from reference **JVM Clojure** in one process. | — |
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| `test/conformance/certify.clj` | Certifies `:expected` against reference **JVM Clojure**; gates on new/stale divergences; emits the profile. | — |
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`corpus.edn` is **JVM-sourced**: `regen-corpus.clj` evaluates each case's `:actual`
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on reference JVM Clojure and writes the JVM value as `:expected`. **`corpus.edn` is
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the canonical, frozen contract**: it is what every runtime consumes, what
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`certify.clj` certifies, and where new cases are authored directly.
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## Row schema
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```edn
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{:suite "numbers / arithmetic" ; grouping; "<suite> :: <label>" is the case id
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:label "integer add" ; unique within a suite
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:actual "(+ 1 2)" ; Clojure source to evaluate
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:expected "3"} ; Clojure source whose value it must equal,
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; or the keyword :throws
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```
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- `[:suite :label]` is the **canonical, unique case id** (the generator
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disambiguates duplicate labels with ` (N)`).
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- Comparison is **value-equality** (`=`), never string/printed-form — so map/set
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iteration order never matters.
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- Because comparison is `=`, a **type** or **laziness** difference is invisible to a
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plain value row: `(= [0 1] '(0 1))` is true, so a fn returning a vector where
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Clojure returns a seq still passes. Pin those explicitly — container/element type
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with a predicate row (`(seq? …)`, `(vector? …)`, `(every? seq? …)`), and laziness
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with a `(take n (… (range)))` row over an infinite source (it hangs, not just
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diverges, if the fn isn't lazy). The `seq / lazy over infinite` suite does both.
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- `:expected :throws` asserts evaluating `:actual` raises.
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## The oracle: reference JVM Clojure
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Historically every `:expected` was hand-written. `certify.clj` removes that
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weakness: it evaluates every `:actual` (and `:expected`) on **JVM Clojure** in a
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fresh `user` namespace and checks jolt's `:expected` against what real Clojure
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produces. Of ~2740 vanilla-certifiable rows, **>2730 match reference Clojure
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exactly**. The rest are classified (see below) — none are silently wrong.
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```sh
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clojure -M test/conformance/certify.clj # gate
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clojure -M test/conformance/certify.clj test/chez/corpus.edn --edn r.edn # + report
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clojure -M test/conformance/certify.clj test/chez/corpus.edn --profile test/conformance/profile.edn
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```
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The gate fails only on a **new** (unclassified) divergence or a **stale**
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allowlist entry; flaky timing-dependent cases (`future-cancel`) are tolerated.
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## Conformance levels & the feature profile
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Not every case is portable: some assume a host capability jolt has on one runtime
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but not another (Java interop, real threads, BigDecimal). `profile.edn` classifies
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each **non-portable** case by the feature it requires. Cases *not* in the profile
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are **portable** — they must pass on any faithful Clojure.
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A runtime's **conformance level** = portable cases + the feature families it
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implements. Current profile (≈2735 portable, ≈167 non-portable):
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| Feature | Meaning |
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|---------|---------|
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| `:numerics/double-only` | all-double numeric model — no Ratio/BigDecimal/float; `(/ 1 2)` ⇒ `0.5` |
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| `:concurrency/snapshot` | isolated-heap futures/agents/pmap — captured atoms are snapshotted, not shared |
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| `:host/jvm-interop` | Java classes / `instance?` on host classes / proxy / bean / definterface |
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| `:host/arrays` | Java arrays (`into-array`, `int-array`, …) |
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| `:async/core-async` | `clojure.core.async` channels/`go` |
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| `:runtime/eval` | runtime `eval` / `load-string` |
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| `:reader/jolt` | jolt reader features (`#?(:jolt …)`) + syntax-quote literal collapse |
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| `:printer/jolt` | jolt's rendering of transients/atoms/`print-method` overrides |
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| `:strictness/jolt` | intentionally stricter (throws on odd `assoc!` args, etc.) |
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| `:impl/representation` | representation detail (e.g. syntax-quote yields a `list?`, not a `Cons`) |
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| `:bug` | a *known defect* (tracked bead) — not a host difference |
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## Seq semantics
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Values alone don't pin laziness — an eager `map` and a lazy `map` return the same
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elements. The spec certifies seq *semantics* by reducing them to values with a
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side-effect counter, so the corpus catches a laziness regression the value
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comparison would miss.
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**Laziness (certified — jolt matches JVM).** The whole producer family
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(`map`/`filter`/`remove`/`take`/`drop`/`concat`/`take-while`/`drop-while`/`mapcat`/
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`partition`/`partition-all`/`partition-by`/`keep`/`keep-indexed`/`map-indexed`/
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`distinct`/`interpose`/`interleave`/`take-nth`/`reductions`/`tree-seq`/`replace`)
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is lazy at construction: building over a side-effecting source realizes **zero**
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elements (`lazy / family is lazy at construction`). Realization order is
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left-to-right, `take`/`nth`/`drop` realize exactly as far as demanded, a lazy seq
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memoizes (realize-once across walks), and `next` realizes head + one lookahead
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while `rest` realizes only the head (`lazy / realization order & count`,
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`lazy / realization is memoized`, `lazy / realization timing`). A lazy result is
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`clojure.lang.LazySeq`.
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**Accepted divergences.** jolt is a simpler, finer-grained superset of JVM seq
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behavior; two classes diverge by representation, never by value, and are
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allowlisted in `known-divergences.edn`:
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- **`:seq-type-model`** (`seq-type-model / …` suite, jolt-aei7) — jolt reifies
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every seq as `PersistentList` (eager) or `LazySeq` (deferred). JVM has a
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specialized class per producer (`Cons`, `Iterate`, `LongRange`, `Repeat`,
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`Cycle`, `PersistentVector$ChunkedSeq`, `StringSeq`, `KeySeq`/`ValSeq`, `RSeq`,
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`ArraySeq`, `SubVector`), so `(class …)` differs. `instance?
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clojure.lang.ISeq/Sequential` and all values/laziness are correct.
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- **`:chunking-model`** (`chunking-model / …` suite, jolt-mm6v) — jolt seqs are
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unchunked: forcing one element realizes one, where JVM realizes a ~32-element
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chunk; `mapcat`/`dedupe` realize 0 at construction where JVM forces the first
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chunk. Strictly finer-grained laziness, decided after the chunk fast path
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(jolt-j9dz) was made O(n).
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## Narrow integer types
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jolt unifies every integer as one exact-integer type (`:integer-box-model`,
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jolt-k9sw). `(byte n)`/`(short n)`/`(int n)` produce value-correct integers —
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arithmetic, `=`, and `hash` behave exactly as the JVM — but report `Long`, not
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`Byte`/`Short`/`Integer`, so `(class (byte 5))` and `(instance? Byte (byte 5))`
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diverge. This is substrate-inherent: a Chez fixnum is an immediate `identical?`
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to the plain integer (nothing to tag, and numbers carry no metadata), so the only
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faithful representation is a boxed type — which would crash the compiled
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arithmetic fast path (both operands Chez numbers → the raw Chez op) or force
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every `+`/`-`/`*` through an unwrapping dispatcher, de-optimizing all
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arithmetic. Same shape as the accepted BigInt-vs-Long unification.
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## Number operations
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Binary arithmetic and comparisons follow the JVM's `Numbers.ops(x, y)` category
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dispatch. Every position (call, value, higher-order) funnels a binary op through
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one seam (`host/chez/seq.ss`): operands inside Chez's tower take the native op
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with the JVM contagion rules patched in; an operand outside it (BigDecimal)
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falls to a slow hook the numeric shim extends (`host/chez/java/bigdec.ss`); a
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non-numeric operand throws `ClassCastException`. The rules the corpus pins
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(`numbers / ops dispatch`, `numbers / with-precision`, `numbers / rationalize`):
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- A double operand wins: `(* 1.0 0)` is `0.0` (Chez's exact-zero shortcut must
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not leak), `(* ##Inf 0)` is `##NaN`, `(+ 1.5M 2.0)` is `3.5`.
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- Division: an exact zero divisor throws `ArithmeticException`; a double zero
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divisor yields `##Inf`/`##-Inf`/`##NaN`. `(/ 1M 3M)` with no bound
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`*math-context*` throws (non-terminating); under `with-precision` it rounds.
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- `quot`/`rem`/`mod` cover the full tower (ratios truncate; doubles keep double;
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`mod` takes the divisor's sign; zero divisor throws in both worlds).
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- `min`/`max` return the *original* operand (`(min 1 2.0)` is `1`, exact); a
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`##NaN` operand wins.
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- `with-precision` binds `*math-context*`; BigDecimal results round to the
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precision with the `java.math.RoundingMode` semantics (default `HALF_UP`,
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`UNNECESSARY` throws).
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- `rationalize` routes a double through its shortest decimal print
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(`BigDecimal.valueOf`), so `(rationalize 1.1)` is `11/10`, not the exact
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binary expansion.
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## Hosting jolt on a new runtime
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1. Implement the reader + analyzer + a backend for your runtime (see the Chez port
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under `host/chez/` for a worked example).
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2. Write a ~30-line harness that, for each corpus row, evaluates `:actual` and
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`:expected` and compares by value-equality (skip `:throws` rows to an
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expect-raises check). Pseudocode:
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```
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(doseq [{:keys [suite label actual expected]} (read-edn "test/chez/corpus.edn")]
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(let [feats (profile-features [suite label])] ; from profile.edn
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(when (subset? feats my-implemented-features) ; only cases I claim to support
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(record! [suite label]
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(if (= :throws expected)
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(raises? actual)
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(value= (eval actual) (eval expected)))))))
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```
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3. Run it. Your **conformance level** is the set of feature families with no
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failures. Portable-only is the floor; each feature you implement raises it.
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The reference harness does exactly this on Chez: `host/chez/run-corpus.ss` (the
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analyzer runs on Chez → Chez runtime), with a regression floor. Run it via `make
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corpus`.
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## Maintaining the spec
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- **Add/change cases**: edit `test/chez/corpus.edn` directly, then re-source the
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answers with `regen-corpus.clj`.
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- **Re-certify**: `clojure -M test/conformance/certify.clj`. A new divergence is
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either a real bug (file it, mark the allowlist entry `:bug` + `:bead`) or a
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deliberate delta (classify it in `known-divergences.edn`).
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- **Refresh the profile**: re-run with `--profile test/conformance/profile.edn`.
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- **Re-floor the runtime gate** when parity rises (`host/chez/run-corpus.ss`).
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