bug#57639: [PATCH] Add new command 'toggle-theme'

[Philip Kaludercic]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Philip Kaludercic <philipk@posteo.net>
>> Cc: larsi@gnus.org,  57639@debbugs.gnu.org
>> Date: Sun, 18 Sep 2022 09:38:02 +0000
>> 
>> >> >> +  (let* ((theme (car custom-enabled-themes))
>> >> >> +         (family (plist-get (get theme 'theme-properties) :family)))
>> >> >> +    (unless family
>> >> >> +      (error "`%s' is not part of a family" theme))
>> >> >
>> >> > "Family"? this terminology was never mentioned in the manual or the
>> >> > doc string.  How about
>> >> >
>> >> >   Theme `%s' does not have any variants
>> >> >
>> >> > instead?
>> >> 
>> >> Strictly speaking that error message would be wrong at this point,
>> >> because we cannot say if a theme has no variants if it is not part of a
>> >> family.  This is because variants of a theme are all those that are part
>> >> of the same family.  I think it would be better to clarify this in the
>> >> documentation.
>> >
>> > But the documentation doesn't explain what it means for a theme to be
>> > part of a family.  Specifically, how does one tell, by looking at a
>> > theme, whether it is or isn't part of a family?
>> >
>> > An alternative for what I suggested above is to say
>> >
>> >   Theme `%s' does not have any known variants
>> 
>> I get what you mean... how about
>> 
>>     (error "Theme `%s' is not part of a family of variants" theme)
>> 
>> ?
>
>   Theme `%s' is not part of a family of theme variants
>
>> >> +Themes only have variants if they are part of a family of themes.
>> >
>> > This should explain what it means to be part of a family, otherwise
>> > this sentence is not helpful.
>> 
>> My intention was for this to be an explanation.  The issue is that
>> variants and family are mutually recursive concepts:
>> 
>> - A variant of a theme are those which are part of the same family
>> - A family of themes is the set of all variants of a theme.
>> 
>> Perhaps it is just easier to collapse both concepts into either variant
>> of family and just "expose" by documenting it.  I've tried doing so
>> below.
>
> Here's an attempt to explain what is a "family", in case it can still
> be of interest:
>
>   A @dfn{family} of themes is a set of similar themes that differ by
>   minor aspects, such as face colors that are meant for the light vs
>   dark background of the frame.

I personally think it is better to omit this for now.  Perhaps this can
be mentioned if or when the theme tags are formalised.