compute-restarts (original) (raw)

ANSI Common Lisp 9 Conditions 9.2 Dictionary of Conditions

Syntax:

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-restartwhen 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 bycompute-restarts is every [should be _ever_] 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%" 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)) (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

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".