Re: music function to be included somewhere in scm/*

[Alexander Kobel]

Hi Knut, hi all.

On 2016-12-14 10:16, Knut Petersen wrote:
> Hi everybody!
>
> There is a discussion on lilypond-user with the target to allow
> automated lyric extenders to lilypond. One part of that is a patch
> to clean and extend lyric_extender.cc.

Knut is playing down his work here. The crucial point: with his patch, 
there is no harm in adding lyric extenders everywhere, because they will 
not produce any output on non-melismata (unless overriden specifically). 
Also, the handling of extender's minimum-length is cleaned up.

> To allow automated creation of lyric extenders a helper function is
> needed

... that does exactly this, adding extenders everywhere.

IMHO, the actual question to decide upon is: Do we want this to be 
enabled by default? IIUC, the fact that extenders are not automatic is a 
known shortcoming. NR 2.1.1 states under "Known issues and warnings":
"Extender lines under melismata are not created automatically; they must 
be inserted manually with a double underscore." (see 
http://lilypond.org/doc/v2.19/Documentation/notation/common-notation-for-vocal-music#multiple-notes-to-one-syllable)

With Knut's patch, this will mostly impact scores where extenders are 
left out unintentionally. Still, it will be a burden for convert-ly 
unless we have a global (or per lyric definition) \noAutomaticExtender 
rule that is inserted by default.

On the other hand, there is the chance to get rid of scores where users 
don't add extenders simply because they are not aware of their 
importance or the proper syntax.


> Putting the
> following code into a lilypond score does the job:
>
> #(define autoextenders (define-music-function (lyrics) (ly:music?)
>    (music-map
>      (lambda (event)
>        (if (and (eq? (ly:music-property event 'name) 'LyricEvent)
>           (not (let* ((art (ly:music-property event 'articulations))
>                       (is-hyphen? (lambda (ev) (eq? (ly:music-property
> ev 'name) 'HyphenEvent))))
>                (find is-hyphen? art)))
>           (not (string=? (ly:music-property event 'text) " ")))
>           (ly:music-set-property! event 'articulations
>              (append (ly:music-property event 'articulations) (list
> (make-music (quote ExtenderEvent))))) event )
>      event)
>    lyrics)))
>
> Q1: Where should a definition of \autoextenders reside?
> scm/music-functions.scm?

AFAICS: yes.

> Q2: Obviously the definition of \autoextenders does not match the coding
> style used in scm/*. It does not even
> work if it is added to music-functions.scm. Some advice is needed ...
> the extending-manual is not a real help in
> this case.

I think you mixed up define-music-function and a plain Scheme define.
IIUC, define-music-function creates an anonymous function with some 
syntactic sugar (e.g., type-checking of the additional arguments past 
parser and location) which is then assigned to a variable:

function = #(define-music-function
             (parser location arg1 arg2)
             (arg1-type-check? arg2-type-check?)
             ...)

That's used in user space and relies on Lilypond's parser, for the 
assignment of the anonymous function. So if we use that, it must go to 
some .ly file with my original syntax; e.g. ly/lyrics-tkit.ly, is apt.

Otherwise, it can go to a .scm file as just
(define (autoextenders lyrics)
 (music-map ...))


Cheers,
Alexander