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  ANSI Common Lisp   9 Conditions   9.2 Dictionary of Conditions

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.

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 [should be ever] 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
 ;; 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

Allegro CL Implementation Details:
No implementation details. We have noted a typo in the sentence just above the Examples: the ANS says "if the list returned by compute-restarts is every modified" and should say "if the list returned by compute-restarts is ever modified".

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