https://gitter.im/http4s/http4s?at=5bbdb915600c5f6423829ebf

generic.scala

 def  genericgeneric[[FF[_]: [_]: MonadErrorMonadError[?[_], [?[_], ThrowableThrowable], ], GG[_]: [_]: TraverseTraverse, , AA](
    gfa: ](     gfa: GG[[FF[[AA]],
    append: ]],     append: GG[[AA] => ] => AA =>  => GG[[AA],
    ref: ],     ref: RefRef[[FF, , GG[[AA]]
): ]] ): FF[[GG[[AA]] =
  gfa
    .traverse(_.attempt.flatTap {
      ]] =   gfa     .traverse(_.attempt.flatTap {       casecase  RightRight(x) => ref.update(append(_)(x))
      (x) => ref.update(append(_)(x))       casecase  LeftLeft(_)  => (_)  => ApplicativeApplicative[[FF].unit
    }.rethrow)
    .handleErrorWith(_ => ref.get)].unit     }.rethrow)     .handleErrorWith(_ => ref.get)
      
 generic[IO, List, String](list2, g => x => g :+ x, ref)

traverse-until-first-failure.scala

val ioa = IO.sleep(1.second) *> IO.pure("a")
val iob = IO.pure("b")
val ioc = IO.pure("c")
val iod = IO.sleep(3.seconds) *> IO.pure("d")
val ioe = IO.sleep(2.seconds) *> IO.pure("e")

val list1 = List(ioa, iob, ioc, iod, ioe)
val list2 = List(ioa, iob, IO.raiseError(new Exception("boom")), iod, ioe)

def collectSuccessful(list: List[IO[String]])(ref: Ref[IO, List[String]]): IO[List[String]] =
  list
    .traverse(_.attempt.flatTap {
      case Right(x) => ref.update(_ :+ x)
      case Left(_)  => IO.unit
    }.rethrow)
    .handleErrorWith(_ => ref.get)

val program = Ref.of[IO, List[String]](List.empty).flatMap { ref =>
  collectSuccessful(list2)(ref).flatMap(x => IO(println(x)))
}