Info Catalog elisp: Function Debugging elisp: Debugger elisp: Using Debugger

elisp: Explicit Debug

 
 17.1.4 Explicit Entry to the Debugger
 -------------------------------------
 
 You can cause the debugger to be called at a certain point in your
 program by writing the expression ‘(debug)’ at that point.  To do this,
 visit the source file, insert the text ‘(debug)’ at the proper place,
 and type ‘C-M-x’ (‘eval-defun’, a Lisp mode key binding).  *Warning:* if
 you do this for temporary debugging purposes, be sure to undo this
 insertion before you save the file!
 
    The place where you insert ‘(debug)’ must be a place where an
 additional form can be evaluated and its value ignored.  (If the value
 of ‘(debug)’ isn’t ignored, it will alter the execution of the program!)
 The most common suitable places are inside a ‘progn’ or an implicit
 ‘progn’ (Sequencing).
 
    If you don’t know exactly where in the source code you want to put
 the debug statement, but you want to display a backtrace when a certain
 message is displayed, you can set ‘debug-on-message’ to a regular
 expression matching the desired message.
 

Info Catalog elisp: Function Debugging elisp: Debugger elisp: Using Debugger