def nat.of
import yaml-for-bend@0.1.1.0/scan.bend as Scanimport Base
1252def nat.of(s: String, acc: Nat) -> Nat:
1253 match s:
1254 case SNil{}:
1255 acc
1256 case SCon{c, t}:
1257 nat.of(t, Nat.add(Nat.mul(acc, 10n), digit.value(c)))