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)

You several options available to you:

// Technique 1 - simple if

for{
  u <- UserStore.getFull(requesterRef)
  _ <- if (u.status == Statuses.Active) unitWriteResult
       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)

// Technique 2 - "monadic if"

for{
  u <- UserStore.getFull(requesterRef) ifM(_.status == Statuses.Active) onTrueMap(_.successPoint(Private)) onFalse(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)

// Technique 3 - "monadic 'when'"

for{
  u <- UserStore.getFull(requesterRef) when(_.status != Statuses.Active) apply 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