When the collection-type inference proves an argument's type, number?/
string?/keyword?/record?/nil?/some? fold to a compile-time boolean. A
const-fold now runs after inference so a folded predicate propagates and
collapses any if it gates to the taken branch.
Sound by construction: only a provable answer folds, and only when the
argument is side-effect-free (a const or local) so dropping its evaluation
is a no-op. Unknown types (:any/:truthy) and impure args keep the call.
vector?/set?/map? are left out — the :vec tag conflates a real vector with
a range/seq, so vector? could be wrong.
50M-iter loop, same shape isolated with a carry-only control: number? call+
branch 5080ms, predicate folded 1365ms — matching the 1417ms control floor,
so the 3.7x is entirely the eliminated call+branch.
Co-authored-by: Yogthos <yogthos@gmail.com>
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