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program-error

program-error Condition Type

Class Precedence List:

program-error, error, serious-condition, condition, t

Description:

The type program-error consists of error conditions related to incorrect program syntax. The errors that result from naming a go tag or a block tag that is not lexically apparent are of type program-error.

Expanded Reference: program-error​

Type Hierarchy​

program-error is a subtype of error that represents errors resulting from incorrect program syntax or semantics detected at runtime (e.g., wrong number of arguments, invalid keyword arguments).

(subtypep 'program-error 'error)
=> T
=> T
(subtypep 'program-error 'condition)
=> T
=> T

Handling program-error with handler-case​

A program-error may be signaled when calling a function with the wrong number of arguments or with invalid keyword arguments.

;; Calling a function with wrong number of arguments
(handler-case
    (funcall (lambda (x) x) 1 2 3)
  (program-error (c)
    (format nil "Caught program-error: ~A" c)))
;; => "Caught program-error: ..."  (message is implementation-dependent)

Checking with typep​

You can inspect a captured condition to confirm it is a program-error.

;; Capture and inspect the condition
(let ((condition
        (handler-case
            (funcall (lambda (x) x))  ; too few arguments
          (error (c) c))))
  (values (typep condition 'program-error)
          (typep condition 'error)))
=> T
=> T

Signaling program-error Manually​

You can signal a program-error in your own code to indicate a static programming mistake.

(defun validate-mode (mode)
  (unless (member mode '(:read :write :append))
    (error 'program-error
           :format-control "Invalid mode: ~S. Expected :READ, :WRITE, or :APPEND."
           :format-arguments (list mode))))

(handler-case (validate-mode :delete)
  (program-error (c)
    (format nil "Caught: ~A" c)))
;; => "Caught: ..."  (message is implementation-dependent)