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bug#33601: 26; Add macro `with-hook-added'
From: |
Alan Mackenzie |
Subject: |
bug#33601: 26; Add macro `with-hook-added' |
Date: |
Tue, 4 Dec 2018 20:10:48 +0000 |
User-agent: |
Mutt/1.10.1 (2018-07-13) |
Hello, Drew.
On Tue, Dec 04, 2018 at 11:18:29 -0800, Drew Adams wrote:
> > > Enhancement request: Please consider adding a macro such as this, to
> > > facilitate temporary use of a hook function.
> > > (defmacro with-hook-added (hook function &rest body)
> > > "Evaluate forms in BODY with FUNCTION added to HOOK, then remove
> > > FUNCTION."
> > > (declare (indent 1) (debug t))
> > > `(unwind-protect (progn (add-hook ',hook ',function) ,@body)
> > > (remove-hook ',hook ',function)))
> > Just a big point: you need to test whether FUNCTION is already on HOOK
> > at the start, and if so, not remove it at the end.
> Hi Alan,
> A big point? Need to?
I think so, yes. The essence of the `with-...' macros is that they
temporarily change something, then evaluate ,@body, and at the end, the
something is restored to what it was.
If with-hook-added didn't preserve the hook, it would be an anomaly, an
outlier, and quite possibly a PITA.
> That wasn't the behavior I had in mind for this, but it's
> another possibility. I intended to provide only for the
> behavior of always removing at the end.
Why? What's the use case?
> There are in fact several different possibilities for such
> a macro. We could provide also for `add-hook' args APPEND
> and LOCAL. I left that out as well.
> Choices:
> 1. Provide a single macro for all such possibilities, with
> 3 (mandatory) args for APPEND, LOCAL and whether to remove
> FUNCTION at the end if it was already present at the outset.
> 2. Provide multiple macros, each specific for a given case.
> #2 would mean 8 macros, to cover all the combinations
> (nil or t for each of the 3 args).
How many of these would actually be of any use?
> Another possibility would be to accept a single arg for
> the BODY code, instead of that being a &rest parameter,
> and so be able to provide those 3 behavior-specifying
> args as optional. In that case, we'd want to decide on
> the best order among those args, e.g., based on which we
> expect to be used most often.
> I'm not sure what the right approach is. I think the
> most common use case would be the one I wrote up (but
> I don't know that):
> . Always remove FUNCTION at the end
> . Prepend, not append.
> . Global, not local.
--
Alan Mackenzie (Nuremberg, Germany).
bug#33601: 26; Add macro `with-hook-added', Glenn Morris, 2018/12/03
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