Kind2/base/List/update_at.kind

List.update_at<A: Type>(index: Nat, fn: A -> A, list: List<A>): List<A>
  case list{
    nil : List.nil!
    cons: case index{
      zero: List.cons!(fn(list.head), list.tail)
      succ: List.cons!(list.head, List.update_at<A>(index.pred, fn, list.tail))
    }
  }