procedure main(arglist)
queue := []
write("Usage:\nqueue x x x - x - - - - -\n\t- pops elements\n\teverything else pushes")
write("Queue is:")
every x := !arglist do {
   case x of {
      "-"     : pop(queue)  | write("pop(empty) failed.")    # pop if the next arglist[i] is a -
      default : put(queue,x)                                 # push arglist[i]
      }
   if empty(queue) then writes("empty")
   else every writes(!queue," ")
   write()
   }
end

procedure empty(X)        #: fail if X is not empty
if *X = 0 then return
end