Re: How to make a tweak a variable?

[David Kastrup]

Xavier Scheuer <address@hidden> writes:

> On 18 September 2011 00:43, David Kastrup <address@hidden> wrote:
>>
>> Use a music argument.  This will, however, only work if the music
>> function is recognizable as a postevent, namely as
>>
>> notToBarline = #(define-music-function
>>  (parser location grb)
>>  (ly:music?)
>> #{
>>  -\tweak #'to-barline ##f-$grb
>> #})
>>
>> {
>> c1-\notToBarline \< |
>> d4\!  % etc.
>> }
>
> Thanks for this answer.
> So IIUC the dash between the end of the tweak and the ly:music?
> argument is mandatory,

No.  If you use notToBarline somewhere else than a postevent, you'll get
a difference in behavior.  Writing -$grb will give you a syntax error
inside of notToBarline (because you gave put music in the place of a
post event), writing $grb will pass the music right into tweak which
will apply it without hesitation.

If you want \notToBarline to still apply a tweak when used as a
non-postevent, you'll write $grb instead -$grb.  I am not overly fond of
this sort of polymorphism.  One consequence is that music functions used
as postevents need one of -^_ before their call.

> as well as the one between the note and the \notToBarline ?

That one, unfortunately, is indispensible because of the mentioned
polymorphism.

>> At the current point of time, you can put postevents into variables,
>> but music functions work as (and on) postevents only if declared as
>> such.  With the current framework, it would be reasonably simple to
>> implement a define-event-function (if really wanted), but it does
>> need support in parser and lexer.
>
> I would like to be able to get rid of the dash between the note and
> \notToBarline .

> But I do not think it is worth going into huge work only for me to
> meet my aesthetic desire (but if someone else is interested in this
> define-event-function and if this is implemented, I would be happy to
> use it of course).  ;-)

For the last week I have been busy fighting shift/reduce and
reduce/reduce conflicts trying to implement optional music function
arguments in a sane and maintainable way.  I am going to get a sane
framework for this first and see where to go from there.

The polymorphism stuff happens to be a real nuisance for implementing
things.

-- 
David Kastrup