warn (original) (raw)

ANSI Common Lisp 9 Conditions 9.2 Dictionary of Conditions

Syntax:

warn datum &rest arguments nil

Arguments and Values:

datum, arguments - designators for a condition of default type simple-warning.

Description:

Signals a condition of type warning. If the condition is not handled, reports the condition to error output.

The precise mechanism for warning is as follows:

• The warning condition is signaled
  While the warning condition is being signaled, the muffle-warning restart is established for use by a handler. If invoked, this restart bypasses further action by warn, which in turn causes warn to immediately return nil.
• If no handler for the warning condition is found
  If no handlers for the warning condition are found, or if all such handlers decline, then the condition is reported to _error output_by warn in an implementation-dependent format.
• nil is returned
  The value returned by warn if it returns is nil.

Examples:

(defun foo (x) (let ((result (* x 2))) (if (not (typep result 'fixnum)) (warn "You're using very big numbers.")) result)) FOO

(foo 3) 6

(foo most-positive-fixnum) Warning: You're using very big numbers. 4294967294

(setq break-on-signals t) T

(foo most-positive-fixnum) Break: Caveat emptor. To continue, type :CONTINUE followed by an option number. 1: Return from Break. 2: Abort to Lisp Toplevel. Debug> :continue 1 Warning: You're using very big numbers. 4294967294

Side Effects:

A warning is issued. The debugger might be entered.

Affected By:

Existing handler bindings.

*break-on-signals*,*error-output*.

Exceptional Situations:

If datum is a _condition_and if the condition is not of type warning, or arguments is non-nil, an error of type type-error is signaled.

If datum is a condition type, the result of (apply #'make-condition datum arguments)must be of type warning or an error of type type-error is signaled.

See Also:

*break-on-signals*,muffle-warning,signal

Allegro CL Implementation Details:

None.