Make \tweak ... Grob equivalent to \override rather than \once \override

Make \tweak ... Grob equivalent to \override rather than \once \override

This simplifies several uses of tweak for both tweak and override.
When desired, one can use \once \tweak in order to get either tweak or
override-once semantics: in the case of the tweak semantics, \once
will just ignore the contained expression.

[Keith, 2013-10-13 03:27:16]

I'm not sure what you are trying to do, but if you mean to make
 \tweak #'transparent ##t NoteHead
do a permanent override, this code doesn't do that.

This code would make \hide NoteHead always act like \once\hide NoteHead.

https://codereview.appspot.com/14503043/diff/1/ly/music-functions-init.ly
File ly/music-functions-init.ly (right):

https://codereview.appspot.com/14503043/diff/1/ly/music-functions-init.ly#new...
ly/music-functions-init.ly:1473: #{ \once\override #(append a b) = #value #}
You need to make the advertised change here, right?

[dak, 2013-10-13 05:42:18]

Shiver me timbers! Forgot the change itself.  Thanks, Keith.

[janek, 2013-10-15 21:51:22]

Do i understand correctly that with this patch one can use \tweak to achieve
everything that \override does?

[dak, 2013-10-15 22:07:34]

On 2013/10/15 21:51:22, janek wrote:
> Do i understand correctly that with this patch one can use \tweak to achieve
> everything that \override does?

That's not really the main point.  It would have been simple previously to make
\tweak be equivalent to \override rather than \once \override when used on
symbol lists.

\tweak syntax for overrides is not really pretty, but it makes it easy to
implement mixed tweaks/overrides like \hide or \omit.  But there are some
changes which only make sense as a \once\override or a \tweak (like footnotes),
and now one can write \once\tweak without a problem, even when it turns out
\tweak is being indeed used as a \tweak and not as an \override.

It's not really an advertisable feature: it's just making several tools fit the
same handle for convenience, but it's not like the resulting look is
particularly elegant.

[janek, 2013-10-15 22:15:36]

2013/10/16  <dak@gnu.org>:
> That's not really the main point.  It would have been simple previously
> to make \tweak be equivalent to \override rather than \once \override
> when used on symbol lists.
>
> \tweak syntax for overrides is not really pretty, but it makes it easy
> to implement mixed tweaks/overrides like \hide or \omit.  But there are
> some changes which only make sense as a \once\override or a \tweak (like
> footnotes), and now one can write \once\tweak without a problem, even
> when it turns out \tweak is being indeed used as a \tweak and not as an
> \override.
>
> It's not really an advertisable feature: it's just making several tools
> fit the same handle for convenience, but it's not like the resulting
> look is particularly elegant.


Indeed, it's not elegant.  But i hope that one day there will be an
elegant tool that could do everything; this patch is a move in that
direction so i support it despite it being not elegant.

best,
Janek