[PATCH 2/4] emacs: repurpose notmuch-show-archive-thread-internal function for general thread tagging

[Aaron Ecay]

On Sun, 08 Jan 2012 18:49:56 -0800, Jameson Graef Rollins <jrollins at finestructure.net> wrote:
> Thanks so much for the review, Aaron.
> 
> On Sun, 08 Jan 2012 20:08:59 -0500, Aaron Ecay <aaronecay at gmail.com> wrote:
> > A couple of comments on the arguments:
> > - It would be good to make show-next &optional.  This will enable code
> >   to call the fn with only two arguments, and not showing next will be
> >   the default behavior.
> 
> That's a nice idea.  Probably better for a separate patch, though.

This patch introduces show-next as a new argument to the function.  So it
can and should make it &optional, if that is the appropriate semantics
for it to have.

> 
> > - A more lispy way of specifying the sign would be to use a
> >   boolean.  Perhaps you could call this “remove”; a value of ‘t’ would
> >   remove the tag; ‘nil’ would add it.  Moving this argument after ‘tag’
> >   and also making it &optional woudl allow this fn to be called with one
> >   arg to add a tag.  (Maybe this is too minimalist and API, however.) 
> 
> That might be more lispy, but it seems a lot less clear to me.  It might
> save a few keystrokes when coding, but it would definitely make the code
> a lot harder to read ("remove" to add a tag?).  I think I would prefer
> people to give the sign explicitly.

Using a string value makes it harder to interface with other code.  For
example, the prefix argument (C-u) is delivered to emacs commands as a
boolean value (nil if no arg, something truthy if the arg is given).  A
plausible custom end user function/keybinding would be one to add a tag
to the open messages, or remove that tag if the prefix arg is given to
the same command.  (So that ‘d’ deletes and ‘C-u d’ undeletes, for
example.)  In order to do that, the user’s code has to convert the
prefix arg into a string.  Making something “lispy” isn’t just about
code readability/saving keystrokes, but also refers to how well the
code interfaces with the conventions used by the rest of the emacs
environment.

That said, here’s an alternate proposal: provide two functions as the
“external” API, namely ‘notmuch-show-{add,remove}-tag-thread’ (by
parallelism with ‘notmuch-show-{add,remove}-tag’).  These could be
thin wrappers around ‘notmuch-show-tag-thread-internal’, which would
then not be intended to be called by user code.

> 
> > No second set of parens is needed around tag-function.
> 
> Yeah, I've seen this either way.  I guess it's just a stylistic
> choice.

Using double parens is semantically correct, but makes the code less
idiomatic and harder to read (IMO).  To test my intuition, I looked at
‘let’ invocations in the Emacs source that have a non-initialized
variable (because the multiple variable case is hard to grep for).
Double parens are used only 3% of the time (44 double vs 1468 single).
Make of this data what you will.

-- 
Aaron Ecay