Re: Advice on troubleshooting function to "unscroll"

[Will Monroe <wtmonroe.ls@gmail.com>]

Drew,

Thank you for this detailed response.

On 01/25/2015 04:45 PM, Drew Adams wrote:
>> the "problem" was that C-v was bound to another (older?) function.
>
> The command `scroll-up' is indeed older, and it is still usable.
> It is, in fact, the core of the `scroll-up-command' implementation.
>
> (In Emacs, it is often the case that you can use a command
> non-interactively, though this is sometimes explicitly not
> recommended for certain commands.)
>
> `scroll-up-command' was added in Emacs 24.1, to (a) retain the
> `scroll-up' behavior as a separate function, and yet (b) provide
> additional behavior when you scroll interactively, in particular
> the handling of the new (in 24.1) option `scroll-error-top-bottom'.

Interesting.  Given what the author's assumptions of how 'scroll-up' 
should work and how the newer 'scroll-up-command' seems to share some, 
but not all, of that functionality, it would probably be interesting to 
see where they differ.  I may not be expressing this clearly, but you've 
helped to clarify the question I want to answer to be: "why did 
scroll-up-command work where the still useful but not appropriate 
scroll-up did not?"

>
>> I've hesitated from diving into Edebug because there was no
>> "error" as such.  That is, the code "worked" it just didn't do
>> what I intended.
>
> Using the debugger (and debugging generally) is not necessarily
> about finding why Emacs raises a particular error.  (That is the
> particular use of variable `debug-on-error': enter the debugger
> to show a backtrace when an error is raised.)
>
> In addition to Edebug, there is the regular Emacs debugger, aka
> `debug'.  Some of us prefer to use that.  Others prefer to use
> it in some cases but `edebug' in other cases.
>
> Keep in mind too that any debugger does not necessarily tell you
> everything that goes on, and its representation of what happens
> with debugging turned off is not flawless.  In particular, this
> is because using the debugger itself changes what Emacs does.
> (Think of the debugger's buffer display and its handling of
> input events, for example.)
>
> The regular debugger is what you get with `debug-on-entry' and
> by inserting calls to `(debug)' in code to serve more or less as
> breakpoints.  See `C-h f debug' for information about evaluating
> and displaying the results of sexps (cdr ARGS) upon entry into
> the debugger.
>

This is very helpful stuff to consider as I begin to think about what I 
want to accomplish when using Edebug or debugger.

And if I'm being honest about why I did not go to Edebug it's because I 
was anticipating great difficulty reading the backtrace statements.  I 
thought my problem might be compounded by a more general illiteracy in 
that regard...

Thanks again, Drew.  A really helpful answer!

Will