Debug Window

The Debug window contains a listener (with a prompt) where you can enter and evaluate Lisp forms. It also displays debugging information after an error (click here to see the description of the Debug window after an error). Here is the Debug window when there is no error being debugged:

The prompt is a [current package](Number). You can type directly to the prompt, pressing Enter for a newline. If you have entered a complete Lisp expression, pressing Enter evaluates it and the returned value is printed below the entered form. If you have not entered a complete expression, pressing Enter places the cursor on the next line, suitably indented, waiting for more input.

There are various ways to repeat an already typed expression. One quick way is to place the text cursor anywhere within an expression visible in the listener pane and then press ENTER. This will copy the whole evaluated expression to the end of the listener's text (either to the prompt or after any text already entered at the prompt). You can quickly move the text cursor to various previously-evaluated forms by holding down the Control and Alt keys and pressing the up and down arrow keys (this also works without the Control key, though on Windows that can trigger functionality for inserting special characters that's built into Microsoft widget).

You can also use the history dropping outline to retrieve an already entered expression.

The dropping outline to the right under the title bar displays the history of entered Lisp expressions, with the most recent visible. (History can be cleared with the blue arrow icon just to the left of the History dropping outline.) Both expressions which were evaluated and those which were entered and not evaluated (because, e.g., the New Prompt button was clicked before evaluation) appear in the list. Clicking on an item in this drop-down list will paste the expression at the listener's prompt, ready to be evaluated again (after optionally editing it). Clicking the blue arrow at the left of an expression will show the values that were returned, each in a separate line (expressions not evaluated have a gray dot rather than a blue arrow); clicking one of these values will return the value, leaving the variable * bound to the value for further use. Expressions in the history drop-down list may also be manipulated more quickly with the keyboard shortcuts for some of the buttons to the left of the drop-down list; see below for details.

To instead copy a sub-expression of an earlier evaluation to the prompt, hold down the control key and left-click in or next to the expression. Clicking just before an opening parenthesis or just after the corresponding closing parenthesis will copy a list expression that starts or ends with that parenthesis; similarly, clicking just before an opening double-quote character or just after a closing double-quote character will copy a string; otherwise, clicking anywhere on a "word" (a character sequence demarcated by parentheses, spaces, tabs, and/or newlines) will copy that word (such as a symbol or number).

The buttons to the left of the dropping outline work as follows. (Placing the cursor over a button causes the tooltip to display. We identify the buttons by the tooltip description.)

• New Prompt: click to get a new prompt. Any unprocessed input is discarded. In certain cases, the listener can become confused about input. Clicking this button clears that confusion.
• Complete History Expression: if you start typing at the prompt and have matched the beginning of an expression in the history, clicking this button completes the expression. Thus, if you have earlier evaluated (+ 1.2 3.4), entering (+ 1.2 and pressing this button completes the expression to match the earlier input. If more than one expression matches what you type, the initial completion is to the most recent. If the most recent match is not the one you are looking for, then this button may be pressed multiple times successively to retrieve older matches. You are warned if nothing matches your input.
• The arrows (Back in History and Forward in History): move forward or back in the history display. Typically you use these keys to select an earlier expression, and then use either the Paste button to copy the selected expression to the prompt for editing and re-evaluation, or the Paste and Evaluate button to re-evaluate the expression as is. The fastest way to reuse earlier expressions is to use the keyboard shortcuts for these buttons; the shortcuts are shown in the button tooltips.
• Paste and Evaluate (a double line arrow with a tail): paste the current history expression (the visible one) to the prompt and evaluate it.
• Paste (an arrow with a tail): paste the current history expression (the visible one) to the prompt but do not evaluate.
• Evaluate (a double line arrow): evaluate the expression at the prompt (equivalent to pressing Enter). If the expression at the prompt is incomplete, go to the next line, indent appropriately, and wait for further input.
• Clear History (a small blue X): clear everything from the history of evaluated Lisp forms and their returned values. This may be useful before calling get-objects or get-references to examine the heap, so that the garbage collector can first remove this old information from the heap. This command does not trigger a garbage collection itself, though, so you may want to use this button and then call gc before examining the heap. If you are using the inspector, then you may also want to right-click the inspector's background and use its Clear History command for the same reason. Using the Trace Dialog's Clear button may also free old objects if needed.

An additional listener pane can be created by choosing View | New Listener.

Copyright (c) 1998-2022, Franz Inc. Lafayette, CA., USA. All rights reserved.
This page was not revised from the 10.0 page.
Created 2019.8.20.