anchor.diff:      :reader loop-jump-exit-info)))
   
   (define-condition loop-break (loop-jump)
  -  ())
  +  ()
  +  (:documentation
  +   "A condition representing that the an enclosing loop should stop
  +running."))
   
   (define-condition loop-continue (loop-jump)
  -  ())
  +  ()
  +  (:documentation
  +   "A condition representing that an enclosing loop should skip ahead
  +to the next iteration."))
   
   (defmacro jump-level (name &body body)
     (let ((block-label (gensym (symbol-name name)))
  
positive.code:          ,result))))
  
  (defmacro shell-for ((variable word-seq) &body body)
    (let ((result (gensym "RESULT"))
          (value (gensym "VALUE")))
      `(break-level
         (let ((,result (truthy-exit-info)))
           (do-iterator (,value (iterator ,word-seq))
             (setf (env ,variable) ,value)
             (setf ,result (continue-level ,@body)))
           ,result))))
  
  
negative.code:               body)))
  
  (defmacro shell-not (&body body)
    "Invert the exit status returned by the given forms.
  
  This is basically just `invert-exit-info' as a macro."
    `(invert-exit-info (progn ,@body)))
  
  (defmacro shell-and (&body body)
    "Return the first falsey exit status produced by a form in `body'.
  
  When a falsey exit status is produced, this macro will short circut
  and skip the remaining forms."
    (unless body
      (return-from shell-and
        '(truthy-exit-info)))
  