I think that the solution is what you said @sijo: throw an exception. I found a way how to suppress the backtrace that produces a clean output; I only need to figure how to change/suppress the ugly red Error message tag. I looked into the throw code but it’s quite cryptic to me (I’m still sort of a julia neophyte) so I cannot replace that pesky error tag string. At least this solution does what I’m looking for; perhaps I should be content with that.