CLHS: Function COMPUTE-RESTARTS

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Function COMPUTE-RESTARTS

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-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~%" 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.

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:

- CONDITION-RESTARTS:PERMIT-ASSOCIATION

Copyright 1996-2005, LispWorks Ltd. All rights reserved.