How to debug elisp?

Question

Usually the easiest way to debug is to use printf . What can be done to debug emacs-lisp? How can I print something in the emacs editor from elisp? Or is there a way to debug elisp code?

For example, how can I check if the following code is executing in a .emacs file?

 (load "auctex.el" nil tt) 

Answer 1

The debugger (edebug) is pretty easy to use. Go to the function definition and type Mx edebug-defun . The next time it is called, you can execute the code as with any other debugger. Enter ? for a list of key bindings or check out the documentation for edebug .

Answer 2

GNU Emacs has two debuggers:

• edebug - explained in another post here
• debugging

I am using debug . These are common entry points (how to use it):

• Mx debug-on-entry , followed by the function that you want to enter using the debugger.

• Mx toggle-debug-on-error - Enter the debugger when an error occurs.

• Mx toggle-debug-on-quit - Enter a debugger when the user presses Cg .
• Place explicit calls to the debug function in specific places (breakpoints) in your code to enter the debugger in these places:

     (debug)

You go through the debugger with d or c to skip the details of a particular evaluation.

Answer 3

This is useful for printing values.

 (message "Hello (%s)" foo) 

but not so good for data structures. To do this, use

 (prin1 list-foo) 

or (prin1-to-string) to insert it into (message).

Answer 4

The easiest way to debug is to run your code interactively. You can do this in the lisp buffer by placing your dot after the expression and running Cx Ce ( eval-last-sexp ).

As an alternative:

 (message "hello world") 

Ch f message to learn more about the built-in message function. If you create a lot of messages, you can set the message-log-max variable to a larger value.

Answer 5

To answer your questions one by one:

• type something: there are a million ways. (message "Hello") places the string in the echo area; (insert "hello") puts the string in the current buffer at the point ...
• How can I check if the following code is running: I would simply replace "auctex.el" with (say) "frotzumotzulous" (i.e. any line at all, if it does not name the real file), and then see if a message appears about the error. If you do not get an error, then it is clear that the code does not run.