How to debug elisp?

The debugger (edebug) is pretty straight forward to use. Go to the definition of the function, and type M-x edebug-defun. The next time it is called, you'll be able to step through the code as with every other debugger. Type ? for the list of keybindings, or check out the documentation for edebug.

---

There are two debuggers in GNU Emacs:

edebug -- explained in another post here

debug

I use debug. These are common entry points (ways to use it):

M-x debug-on-entry followed by a function you want to enter using the debugger.

M-x toggle-debug-on-error -- Enter the debugger when when an error is raised.

M-x toggle-debug-on-quit -- Enter the debugger when the user hits C-g.

Place explicit calls to function debug at particular places (breakpoints) in your code, to enter the debugger at those places:

(debug)

You step through the debugger using d, or c to skip over the details of a particular evaluation.

---

This is useful for printing values

(message "Hello (%s)" foo)

but doesn't work so well for data structures. For that, use

(prin1 list-foo)

or (prin1-to-string) to embed it in a (message).

---

The easiest way to debug may be to run your code interactively. You can do that in a lisp buffer by placing your point after the expression and running C-x C-e (eval-last-sexp).

Alternatively:

(message "hello world")

C-h f message to find out more about the built in message function. If you generate lots of messages, you may want to customize the variable message-log-max to a larger value.

---

To answer your questions one by one:

print something: there's a million ways. (message "Hello") puts the string in the echo area; (insert "hello") puts the string into the current buffer at point ...

how can I check if the following code is run: I'd just replace "auctex.el" with (say) "frotzumotzulous" (i.e., any string at all, as long as it doesn't name a real file) and then see if you get an error message. If you get no error, then clearly that code isn't being run.

---