Re: An instructive example of trace-function and some example of debugging

[Icarus Sparry]

On Sun, 13 Jun 2010 13:31:32 -0700, bolega wrote:

> On Jun 13, 8:07 am, Icarus Sparry <use...@icarus.freeuk.com> wrote:
>> On Sat, 12 Jun 2010 10:43:46 -0700, bolega wrote:
>> > On Jun 10, 1:27 pm, bolega <gnuist...@gmail.com> wrote:
[snip]
>> > Sometimes, in emacs, error takes places and the mode gets nested
>> > inside many brackets.
>>
>> > [(((.lisp...)))]
>>
>> > above line recalling from memory
>>
>> > what does it mean ? C-g does not get out of it.

>> If you are seeing [[[lisp]]] then you are in a "recursive edit".
>>
>> This is not an error, it is a feature! The most common way to get into
>> it is if you are doing a query-replace (M-% with standard bindings),
>> and type control-r. This allows you to make some edits and then
>> continue the query-replace.
>>
>> The standard key binding to abort out of recursive edit is C-] (the
>> [..] in the mode line is supposed to help you remember this key
>> sequence).
> 
> thx. I searched google ,
> 
> http://groups.google.com/group/gnu.emacs.help/search?
num=100&group=gnu.emacs.help&q=recursive+edit&qt_g=Search+this+group
> 
> but found very sketchy info on how to utilize this FEATURE. Just one
> seemed helpful,
> 
> http://groups.google.com/group/gnu.emacs.help/browse_thread/
thread/8dc303a526356794/96c264702c0a4443?lnk=gst&q=recursive
+edit#96c264702c0a4443
> 
> otherwise people were complaining how to get out of this strangeness,
> even a "high IQ" guy from some big name company.
> 
> Can anyone add useful ideas how to get out of it incrementally and
> really get benefit from it. Is there somewhere a more complete info on
> it ?

As I said, the most common way I use it is when I am doing a query-
replace (or query-replace-regex) and I am stepping through the buffer 
typing space or n to make a change or not. If I notice something that 
needs fixing, then I can type control-r and this suspends the query-
replace and lets me do whatever it takes to fix the problem. Once I have 
done this then I type C-M-c to resume the query-replace.

The emacs info has a section on it.

This also states that if you enter the emacs debugger then this also can 
start a recursive edit, and you can use 'c' to continue from the debugger 
window. There are several ways in which you can enter the debugger, in 
particular evaluating the form

   (debug a)

will print the value of a to the backtrace buffer and enter the debugger.