Re: Please tear apart this example lead sheet template for traditional Western folk tunes

[Valentin Petzel]

Hello Tom,

you accidently forwarded me the digest. Unless there is a reason not to when 
replying to a message please change the Subject to match the discussion, make 
sure to include the list to the recipients and optimally adjust the quoted 
body to not include the whole digest.

If you’ve got any questions about what is happening here feel free to ask. We 
are using here that we can "register" scores to the current book(part) from 
scheme using the function (add-score score) (similarly we can use (add-text 
markup) to add a stand-alone markup to the book). This allows us to construct 
scores using scheme, which makes automated handling of thing much easier.

So what we want to have is a function that creates a score using standard 
elements, that is, chords, a voice, and lyrics. At the same time we want to be 
flexible enough to leave out some of these elements.

So we define a void-function (that is a scheme function that returns nothing) 
that takes:
→ The title of the score
→ Optionally the composer of the score
→ A piece of music for the voice or #f
→ A piece of music for the chords or #f
→ A piece of lyrics (which is also music) or a list of such (to allow stanzas)
     or #f

The syntax here is
myfunction =
#(define-void-function (arg1 arg2 ...)
    (type-check-arg1 type-check-arg1 ...)
    function-body)

where the type-checks are predicates (functions returning truth values) or 
(predicate default) for optional arguments with default value.

We then use let* which allows us to locally bind some variables (similar to 
let, but let* lets each binding access the previous bindings). The syntax here 
is

(let* ((var1 value1) (var2 value2) ...) body)

So we define CN, FB, VC, LY as shorthands for the ChordNames, FretBoards, Voice 
and Lyrics. If one of these is set to #f we use empty-music, which is music 
containing nothing, else we create the contexts with the specified music.

As lyrics might be a list of lyrics we have to handle both of these things, 
which is done by either doing something to the lyrics or by doing to the whole 
list (which is the (map function list) expression). We also need to handle the 
presence of the Voice here. If for some reason voice is set to #f we should 
not align the lyrics to anything and rely on the lyrics themselves being 
rhythmicised. To make further handling easier we make sure that LY is list 
even when lyrics isn’t. [WHICH BY THE WAY I FORGOT IF lyrics IS #f, THIS IS 
FIXED IN THE APPENDED FILE!]

So we get a big expression basically just checking:
→ Is lyrics #f? If so use (in the fixed version a list of) empty music.
→ Is voice #f? If so do not use \lyricsto "auto"
→ Is lyrics music or a list? If so we use map to create Lyrics for each member 
of the list. If not we create a list containing a single Lyrics context.

Next we basically want to put all of these contexts in a << ... >> construct. 
This is known as "simultaneous music" and is internally stored as
(make-music 'SimulataneousMusic 'elements A-LIST-OF-MUSIC)
where the list of music contains the content of ... . This means we simply 
have to construct this list and then do the above call with this list.

I won’t go into detail what a LISP list is, if you are interested please ask 
or checkout what I wrote to Simon earlier this thread. But basically if L is a 
list then `(,a ,b ,c . ,L) will be L with a, b and c prepended. As Jean 
pointed out this can be done by (cons* a b c L).

So we do a
(cons* CN FB VC LY)
to create a list of all the contexts we created so far (and maybe some empty 
music, but we do not really have to care about these).

Next we create a score with the specified header informations and the 
previously created simultaneous music. Using #{ ... #} allows us to parse the 
content between as Lilypond syntax instead of scheme syntax. So we do
#{ \score { ... } #}
and create the score just like we would in Lilypond syntax.

Then the last thing we do is use add-score to add this newly created score to 
the current book.

Cheers,
Valentin

Am Donnerstag, 24. Februar 2022, 00:05:42 CET schrieben Sie:
> Thank you for completely upgrading my lead sheet template. WOW! I haven't
> acknowledged because it's so advanced. You've added a bunch of advanced
> features I'm trying to understand thoroughly.

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