def Array.map.at
import Base2627def Array.map.at(
2628 ~T: Data, ~U: Data, ~f: T -> U, v: U, an: Array<T> & U32
2629) -> Array<U>:
2630 (a, +n) = an
2631 Array.map.go(~T, ~U, ~f, U32.to_nat(U32.sub(n, 1)), 1,
2632 Array.new(U, U32.log2(n), v), Array.get(T, a, 1))