Re: New hosting for Urs Liska's Scheme WIP book

[Jean Abou Samra]

Le 04/11/2022 à 00:13, Karlin High a écrit :
> Could a music function or something be shorthand for that? Let's see...
>
> <https://lilypond.org/doc/v2.23/Documentation/notation/substitution-function-syntax> 
>
>
> That page is pretty ideal. Here's the general form, what it contains, 
> and how it can be used.



Well yes; however, the Scheme tutorials at hand are mostly about
the Scheme language itself, not so much about its integration with
LilyPond. In other words, they're kind of a substitute for this part
of the official documentation:

https://lilypond.org/doc/v2.23/Documentation/extending/introduction-to-scheme

That part is (from experience) mostly useless as a beginner. It
does not even mention let* !


> I ended up with this:
>
> %
> \version "2.23.80"
> uniTwo = #(define-music-function
>            (uniNote)
>            (ly:music?)
>            #{
>              << { \voiceOne #uniNote }
>                 \new Voice { \voiceTwo #uniNote }
>              >> \oneVoice
>            #})
>
> { c'4 \uniTwo e' g' }
> %
>
> I may end up replacing all the chords with the temporary-polyphony 
> construct. And I may get told my \uniTwo function is very far from 
> best practice.




Better use $uniNote for at least one of the two occurrences,
so as to make a copy of the note. Otherwise, you might
have surprises when applying music functions to the result,
because the note is shared. For example:

\version "2.23.80"
uniTwo = #(define-music-function
           (uniNote)
           (ly:music?)
           #{
             % Using $uniNote instead of #uniNote would fix the problem.
             << { \voiceOne #uniNote }
                \new Voice { \voiceTwo #uniNote }
             >> \oneVoice
           #})

% Transposition should yield G notes, but yields B flat notes
% as it is done twice, due to sharing.
\new Staff \transpose e' g' { \uniTwo e' \uniTwo e' }


Also, you will have surprises with \relative because
the note appears twice, with its octave marks. You
can use make-relative to fix that.

So, overall, better do:


\version "2.23.80"

uniTwo =
#(define-music-function (uniNote) (ly:music?)
   (make-relative
    (uniNote)
    uniNote
    #{
      << { \voiceOne $uniNote }
         \new Voice { \voiceTwo $uniNote }
      >> \oneVoice
    #}))

\new Staff \transpose e' g' \relative { \uniTwo e' \uniTwo e' }


Best,
Jean

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