From @src/flow.l

                           (Dst: ca (val $Catch))
                           (Dst: in (val $InFrames))
                           (Dst: out (val $OutFrames))
                           (Dst: err (val $ErrFrames))
                           (Dst: ctl (val $CtlFrames))
                           (putCrtEnv (Dst:))
                           (set  # Init local env
                              $Next $Nil
                              $Make 0
                              $Yoke 0
                              $Current (Dst:)
                              $StkLimit (+ (Dst: lim) 1024) )
                           (when (symb? Tag)
                              (put Tag ZERO (| (i64 (Dst:)) 2)) )
'Dst:' is changed          (set $Ret (run X))
when 'run' returns         (unless (== (hex "0707070707070707") (val (i64* (Dst: lim))))
                              (stkOverErr (Dst: tag)) )
                           (set $This (val -3 (Dst: bnd)))
                           (stop (Dst:))  # Stop coroutine
                           (let Org: (coroutine (Dst: org))
                              (unless (and (Org:) (== (Org: tag) (Dst: otg)))
                                 (coErr Exe (Dst: otg)) )
                              (longjmp (Org: (rst)) 1) ) ) ) ) )