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Syntax:

cerrorcontinue-format-control datum&rest arguments =>nil

Arguments and Values:

Continue-format-control---aformat control.

datum,arguments---designators for acondition of default typesimple-error.

Description:

cerror effectively invokeserror on thecondition named bydatum. As with any function that implicitly callserror, if thecondition is not handled,(invoke-debuggercondition) is executed. While signaling is going on, and while in the debugger if it is reached, it is possible to continue code execution (i.e., to return fromcerror) using thecontinuerestart.

Ifdatum is acondition,arguments can be supplied, but are used only in conjunction with thecontinue-format-control.

Examples:

 (defun real-sqrt (n)   (when (minusp n)     (setq n (- n))     (cerror "Return sqrt(~D) instead." "Tried to take sqrt(-~D)." n))   (sqrt n)) (real-sqrt 4)=>  2.0 (real-sqrt -9)>>  Correctable error in REAL-SQRT: Tried to take sqrt(-9).>>  Restart options:>>   1: Return sqrt(9) instead.>>   2: Top level.>>  Debug> :continue 1=>  3.0  (define-condition not-a-number (error)   ((argument :reader not-a-number-argument :initarg :argument))   (:report (lambda (condition stream)              (format stream "~S is not a number."                       (not-a-number-argument condition)))))  (defun assure-number (n)   (loop (when (numberp n) (return n))         (cerror "Enter a number."                 'not-a-number :argument n)         (format t "~&Type a number: ")         (setq n (read))         (fresh-line))) (assure-number 'a)>>  Correctable error in ASSURE-NUMBER: A is not a number.>>  Restart options:>>   1: Enter a number.>>   2: Top level.>>  Debug> :continue 1>>  Type a number: 1/2=>  1/2 (defun assure-large-number (n)   (loop (when (and (numberp n) (> n 73)) (return n))         (cerror "Enter a number~:[~; a bit larger than ~D~]."                 "~*~A is not a large number."                  (numberp n) n)         (format t "~&Type a large number: ")         (setq n (read))         (fresh-line)))  (assure-large-number 10000)=>  10000 (assure-large-number 'a)>>  Correctable error in ASSURE-LARGE-NUMBER: A is not a large number.>>  Restart options:>>   1: Enter a number.>>   2: Top level.>>  Debug> :continue 1>>  Type a large number: 88=>  88 (assure-large-number 37)>>  Correctable error in ASSURE-LARGE-NUMBER: 37 is not a large number.>>  Restart options:>>   1: Enter a number a bit larger than 37.>>   2: Top level.>>  Debug> :continue 1>>  Type a large number: 259=>  259  (define-condition not-a-large-number (error)   ((argument :reader not-a-large-number-argument :initarg :argument))   (:report (lambda (condition stream)              (format stream "~S is not a large number."                       (not-a-large-number-argument condition)))))  (defun assure-large-number (n)   (loop (when (and (numberp n) (> n 73)) (return n))         (cerror "Enter a number~3*~:[~; a bit larger than ~*~D~]."                 'not-a-large-number                 :argument n                  :ignore (numberp n)                 :ignore n                 :allow-other-keys t)         (format t "~&Type a large number: ")         (setq n (read))         (fresh-line)))  (assure-large-number 'a)>>  Correctable error in ASSURE-LARGE-NUMBER: A is not a large number.>>  Restart options:>>   1: Enter a number.>>   2: Top level.>>  Debug> :continue 1>>  Type a large number: 88=>  88  (assure-large-number 37)>>  Correctable error in ASSURE-LARGE-NUMBER: A is not a large number.>>  Restart options:>>   1: Enter a number a bit larger than 37.>>   2: Top level.>>  Debug> :continue 1>>  Type a large number: 259=>  259

Affected By:

*break-on-signals*.

Existing handler bindings.

Exceptional Situations: None.

See Also:

error,format,handler-bind,*break-on-signals*,simple-type-error

Notes:

Ifdatum is aconditiontype rather than astring, theformat directive~* may be especially useful in thecontinue-format-control in order to ignore thekeywords in theinitialization argument list. For example:

(cerror "enter a new value to replace ~*~s"         'not-a-number        :argument a)

• FORMAT-STRING-ARGUMENTS:SPECIFY