docs: settle the numeric-tower position (#417)#434
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…forced (#417) The only number kind is the IEEE-754 f64, and that is now a documented, decided position rather than an unstated default. SPEC.md gains a "numeric model" subsection stating the contracts it buys, with byte-checked examples: - integer exactness ends at 2^53 (`9007199254740992 + 1` is invisible); - arithmetic is finite by construction — `NaN` collapses to 0 (`sqrt of -1` = 0), overflow saturates at ±1e308, never Infinity; - integer bitwise ops act on int64, exact past 2^32 (`1 << 40`) — the seam for checksums/hashing/byte protocols (the #382 int32-UB saga is why this is spelled out). Decision: bigint/decimal are deferred until a consumer genuinely forces them — they would ripple through the JIT and the AOT (whose numeric speed rests on everything-being-a-double). The wording deliberately avoids overcommitting "num IS f64" so a future wider kind can still honor these contracts. Roadmap item promoted from a one-liner to the decided position. Suite 2509/2509. Closes #417 Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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What
The only number kind is the IEEE-754 f64 — now a documented, decided position rather than an unstated default (the survey's missing-dimension finding). SPEC.md gains a "numeric model" subsection stating the contracts it buys, with byte-checked examples:
9007199254740992 + 1is invisible.NaNcollapses to0(sqrt of -1= 0), overflow saturates at ±1e308, neverInfinity.1 << 40) — the seam for checksums/hashing/byte protocols. (The Stdlib train: num-of hex contract, bit_* int64 alignment, checksum.eigs, datetime civil math #382 int32-UB saga is why this is spelled out explicitly.)The decision
Bigint / decimal are deferred until a consumer genuinely forces them — they'd ripple through the JIT and the AOT (whose numeric speed rests on everything-being-a-double). The wording deliberately avoids overcommitting "num is an f64" so a future wider numeric kind could still honor these same contracts (exactness-below-2^53, finiteness, the int64 seam).
Roadmap item promoted from a one-liner to the decided position. Suite 2509/2509.
Closes #417
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