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(emacs-lisp-intro.info)Debugging Exercises

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Debugging Exercises
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   * Install the `count-words-region' function and then cause it to
     enter the built-in debugger when you call it.  Run the command on a
     region containing two words.  You will need to press `d' a
     remarkable number of times.  On your system, is a `hook' called
     after the command finishes?  (For information on hooks, see Note:
     Command Loop Overview.)

   * Copy `count-words-region' into the `*scratch*' buffer, instrument
     the function for Edebug, and walk through its execution.  The
     function does not need to have a bug, although you can introduce
     one if you wish.  If the function lacks a bug, the walk-through
     completes without problems.

   * While running Edebug, type `?' to see a list of all the Edebug
     commands.  (The `global-edebug-prefix' is usually `C-x X', i.e.
     `<CTL>-x' followed by an upper case `X'; use this prefix for
     commands made outside of the Edebug debugging buffer.)

   * In the Edebug debugging buffer, use the `p'
     (`edebug-bounce-point') command to see where in the region the
     `count-words-region' is working.

   * Move point to some spot further down function and then type the
     `h' (`edebug-goto-here') command to jump to that location.

   * Use the `t' (`edebug-trace-mode') command to cause Edebug to walk
     through the function on its own; use an upper case `T' for
     `edebug-Trace-fast-mode'.

   * Set a breakpoint, then run Edebug in Trace mode until it reaches
     the stopping point.