proc ?lappend {v_name args} {
     upvar $v_name v
     if {![info exists v]} {
         return -code error "expected $v_name to exist!"
     }
     if {[array exists v]} {
         return -code error "can't set \"$v_name\": variable is array"
     }
     foreach val $args {
         lappend v $val
     }
     return $v
}