extension Result {

   @discardableResult
   func ifFailure(_ f: (Failure) -> Void) -> Result {
       if case let .failure(e) = self { f(e) }
       return self
   }
}

extension Result where Failure: OptionSet, Failure == Failure.Element {

   @discardableResult
   func ifFailure(contains error: Failure, _ f: () -> Void) -> Result {
       if case let .failure(e) = self,
           e.contains(error) {
               f()
       }
       return self
   }
}