9.2.32 compute-restarts [Function]

compute-restarts &optional condition ⇒ restarts

Arguments and Values::

condition—a condition object, or nil.

restarts—a list of restarts.

Description::

compute-restarts uses the dynamic state of the program to compute a list of the restarts which are currently active.

The resulting list is ordered so that the innermost (more-recently established) restarts are nearer the head of the list.

When condition is non-nil, only those restarts are considered that are either explicitly associated with that condition, or not associated with any condition; that is, the excluded restarts are those that are associated with a non-empty set of conditions of which the given condition is not an element. If condition is nil, all restarts are considered.

compute-restarts returns all applicable restarts, including anonymous ones, even if some of them have the same name as others and would therefore not be found by find-restart when given a symbol argument.

Implementations are permitted, but not required, to return distinct lists from repeated calls to compute-restarts while in the same dynamic environment. The consequences are undefined if the list returned by compute-restarts is every modified.

Examples::

 ;; One possible way in which an interactive debugger might present
 ;; restarts to the user.
 (defun invoke-a-restart ()
   (let ((restarts (compute-restarts)))
     (do ((i 0 (+ i 1)) (r restarts (cdr r))) ((null r))
       (format t "~&~D: ~A~
     (let ((n nil) (k (length restarts)))
       (loop (when (and (typep n 'integer) (>= n 0) (< n k))
               (return t))
             (format t "~&Option: ")
             (setq n (read))
             (fresh-line))
       (invoke-restart-interactively (nth n restarts)))))

 (restart-case (invoke-a-restart)
   (one () 1)
   (two () 2)
   (nil () :report "Who knows?" 'anonymous)
   (one () 'I)
   (two () 'II))
 |>  0: ONE
 |>  1: TWO
 |>  2: Who knows?
 |>  3: ONE
 |>  4: TWO
 |>  5: Return to Lisp Toplevel.
 |>  Option: |>>4<<|
⇒  II

 ;; Note that in addition to user-defined restart points, COMPUTE-RESTARTS
 ;; also returns information about any system-supplied restarts, such as
 ;; the "Return to Lisp Toplevel" restart offered above.

Affected By::

Existing restarts.

See Also::

find-restart , invoke-restart , restart-bind