how to fail inside for comprehension of actionmonad

gistfile1.scala

    for{
      u <- UserStore.getFull(requesterRef)
            // .map{usr=> if(false) notAuthorizedC("x") else usr}
            .map{usr=>UserRefs.ById(usr.id)}
      // _ <- if (u.status == Statuses.Active) success 
      //      else notAuthorizedC("Unable to retrieve the permissions for post: [%s] and requester: [%s]".format(postRef, requesterRef))
      r <- postRef match {
            case ref:PostRefs.ById => 
              getPermitedOperationsForPostsById(Set(ref), u)
                .map[ReaderCtx, Set[Operation]]{r=> r(ref)}
            case ref:PostRefs.ByPermalink => 
              getPermitedOperationsForPostsByPermalink(Set(ref), u)
                .map[ReaderCtx, Set[Operation]]{r=> r(ref)}
          }
    } yield (r)

@peterjanovsky is probably more correct: better to handle this in SQL first rather than bring it back to the client