Reading an error message

Following is an example of a simple error message. The following code for creating and closing a window contains an error:

Enter an expression which contains an error.

? (setf w (make-instance 'window))
#<WINDOW "Untitled" #x4CF1D1>
? (close-window w)
> Error: Undefined function CLOSE-WINDOW called with
> arguments (#<WINDOW "Untitled" #x4CF1D1>) .
> While executing: TOPLEVEL-EVAL
> Type Command-/ to continue, Command-. to abort.
> If continued: Retry applying CLOSE-WINDOW to 
> (#<WINDOW "Untitled" #x4CF1D1>).
See the Restarts... menu item for further choices.
1 >

In this case there is no such function as close-window. The function toplevel-eval (which is part of the read-eval-print loop) gets an error when trying to call this non-existent function.

The error message first gives the nature of the problem.

> Error: Undefined function CLOSE-WINDOW called with > arguments (#<WINDOW "Untitled" #x4CF1D1>).

The message notes the function in which the error occurred:

> While executing: TOPLEVEL-EVAL

Next the message describes your options for recovery or cancellation. In this case, you can either retry calling the function by choosing Continue, or you can cancel the entire computation with Abort. As always, you can check the Restarts window for additional options. (They keystrokes command-/ and command-. are shortcuts for the Continue and Abort commands on the Lisp menu.)

> Type Command-/ to continue, Command-. to abort. > If continued: Retry applying CLOSE-WINDOW to (#<WINDOW > "Untitled" #x4CF1D1>). See the Restarts... menu item for further choices.

Finally the error message gives you a distinctive prompt notifying you that you are in a break loop. The 1 indicates that you are in the first level of a break loop.
1 >

Gettmg Started with MCL - 19 OCT 1996

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