def point.at
import yaml-for-bend@0.1.1.0/num.bend as Numimport Base
187def point.at(+ip: Nat, e: Exp) -> Nat:
188 match e:
189 case Exp{neg, +n}:
190 Bool.pick(Nat, neg, Nat.sub(Nat.add(dec.off(), ip), n), Nat.add(Nat.add(dec.off(), ip), n))