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(elisp)Infinite Loops

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Debugging Infinite Loops
------------------------

   When a program loops infinitely and fails to return, your first
problem is to stop the loop.  On most operating systems, you can do this
with `C-g', which causes a "quit".

   Ordinary quitting gives no information about why the program was
looping.  To get more information, you can set the variable
`debug-on-quit' to non-`nil'.  Quitting with `C-g' is not considered an
error, and `debug-on-error' has no effect on the handling of `C-g'.
Likewise, `debug-on-quit' has no effect on errors.

   Once you have the debugger running in the middle of the infinite
loop, you can proceed from the debugger using the stepping commands.
If you step through the entire loop, you will probably get enough
information to solve the problem.

 - User Option: debug-on-quit
     This variable determines whether the debugger is called when `quit'
     is signaled and not handled.  If `debug-on-quit' is non-`nil',
     then the debugger is called whenever you quit (that is, type
     `C-g').  If `debug-on-quit' is `nil', then the debugger is not
     called when you quit.  Note: Quitting.