Problem with after-change-functions hook

Problem with after-change-functions hook

[user240]

I am trying to create a hook so as to run a function when a certain buffer
changes. I put this in a mode definition function:

(add-hook 'after-change-functions 'function nil t)

but the resulting hook appears to be global, as the function take effect on
all buffers!? What do I do to restrict the hook to the buffer that the mode
function was run?

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Re: Problem with after-change-functions hook

[Stefan Monnier]

> I am trying to create a hook so as to run a function when a certain buffer
> changes. I put this in a mode definition function:

> (add-hook 'after-change-functions 'function nil t)

Other than the use of the name `function', this looks correct.

> but the resulting hook appears to be global, as the function take effect on
> all buffers!?

That shouldn't be the case.  What makes you think this is the case?
What does C-h v after-change-functions RET say when called in the buffer
(the one where you want the hook to be active)?


        Stefan

Re: Problem with after-change-functions hook

[user240]

In the buffer I want the hook to be active I get:
"
`after-change-functions' is a simple built-in variable.

Value: (function)

Documentation:
List of functions to call after each text change.
Three arguments are passed to each function: the positions of
the beginning and end of the range of changed text,
and the length of the pre-change text replaced by that range.
(For an insertion, the pre-change length is zero;
for a deletion, that length is the number of characters deleted,
and the post-change beginning and end are at the same place.)

Buffer changes made while executing `after-change-functions'
don't call any before-change or after-change functions.
"

and the same for every other buffer, including the minibuffer.
note - I'm using xemacs 21.4.17 in Ubuntu linux.
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Re: Problem with after-change-functions hook

[Stefan Monnier]

> In the buffer I want the hook to be active I get:
> "
> `after-change-functions' is a simple built-in variable.

> Value: (function)

[...]

> and the same for every other buffer, including the minibuffer.
> note - I'm using xemacs 21.4.17 in Ubuntu linux.

In this case I'd first use another name than `function' (this may be the
cause of your problems, and it's an extremely bad choice in any case).

Then I'd try to call `make-local-hook' before add-hook.

And if that doesn't help, I'd ask on compe.emacs.xemacs because it may
simply be a behavior that's different on XEmacs.


        Stefan

Re: Problem with after-change-functions hook

[user240]

I'd don't actually use that name, I just used it to [paraphrase?] my code.
I have also used different and unique names instead, and the problem
persisted.
The manual says that using 't' as the optional local argument is equivolent
to using the make-local-hook function.
My problem might be a peculiarity of xemacs, but it seems unlikely. I will
test the same code with emacs (nox) soon.

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Re: Problem with after-change-functions hook

[Stefan Monnier]

> The manual says that using 't' as the optional local argument is equivolent
> to using the make-local-hook function.

Which manual?  This is true for Emacs >= 21, but not for Emacs-20 and maybe
not for XEmacs either, or at least not for all versions.


        Stefan