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compute-restarts &optional condition => restarts

Arguments and Values:

condition---a condition object, or nil.

restarts---a list of restarts.


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.


 ;; 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~%" i (car r)))
     (let ((n nil) (k (length restarts)))
       (loop (when (and (typep n 'integer) (>= n 0) (< n k))
               (return t))
             (format t "~&Option: ")
             (setq n (read))
       (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.

Side Effects: None.

Affected By:

Existing restarts.

Exceptional Situations: None.

See Also:

find-restart, invoke-restart, restart-bind

Notes: None.

The following X3J13 cleanup issue, not part of the specification, applies to this section:

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