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conformance: document narrow-int unification (byte/short/int -> Long)

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jolt unifies every integer as one exact-integer type, so (byte/short/int n)
report Long not Byte/Short/Integer and instance? Byte is false. Confirmed
substrate-inherent: (byte 5) is a Chez immediate identical? to 5 (nothing to
tag, numbers carry no metadata), and arithmetic compiles to a raw Chez + that a
boxed narrow type would crash. Value/arithmetic/equality are correct.

Certify the value-correctness (= to plain int, arithmetic promotes, is a Number)
and pin the class/instance? divergence under a new :integer-box-model category.
Data/doc only.
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Yogthos 2026-06-28 10:28:10 -04:00
parent 59cfa5f53f
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test/conformance/SPEC.md
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@ -119,6 +119,19 @@ allowlisted in `known-divergences.edn`:
chunk. Strictly finer-grained laziness, decided after the chunk fast path
(jolt-j9dz) was made O(n).
## Narrow integer types
jolt unifies every integer as one exact-integer type (`:integer-box-model`,
jolt-k9sw). `(byte n)`/`(short n)`/`(int n)` produce value-correct integers —
arithmetic, `=`, and `hash` behave exactly as the JVM — but report `Long`, not
`Byte`/`Short`/`Integer`, so `(class (byte 5))` and `(instance? Byte (byte 5))`
diverge. This is substrate-inherent: a Chez fixnum is an immediate `identical?`
to the plain integer (nothing to tag, and numbers carry no metadata), so the only
faithful representation is a boxed type — which would crash raw compiled `(+ …)`
(arithmetic emits a bare Chez `+`) or force every `+`/`-`/`*` through an
unwrapping dispatcher, de-optimizing all arithmetic. Same shape as the accepted
BigInt-vs-Long unification.
## Hosting jolt on a new runtime
1. Implement the reader + analyzer + a backend for your runtime (see the Chez port