How to debug elisp?
DebuggingEmacsElispDebugging Problem Overview
Normally the easiest way to debug is using printf. What can I do to debug emacs-lisp? How can I print something to emacs editor from elisp? Or is there any way to debug elisp code?
For example, how can I check if the following code is run in .emacs file?
(load "auctex.el" nil t t)
Debugging Solutions
Solution 1 - Debugging
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.
Solution 2 - Debugging
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-entryfollowed 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
debugat 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.
Solution 3 - Debugging
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).
Solution 4 - Debugging
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.
Solution 5 - Debugging
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.