let addChild updateNode addNode value parent =
  match withNewChild value parent with
  | None -> async.Return None
  | Some (newParent, child) as path ->
    async { do! addNode child
            do! updateNode newParent
            return Some child }

let addChildById getNode updateNode addNode logAction value parentId =
  async { let! parent = getNode parentId
          let! childOpt = addChild updateNode addNode value parent
          match childOpt with
          | None -> return None
          | Some child ->
            let action = AddNode { value = value; nodeId = nodeId; leafId = child.id }
            do! logAction action
            return Some child.id }