Re: [SPAM] Re: Generating a (#:column ...) list in Scheme

[Urs Liska]

Hi David,

thanks for the assistance.

Am 08.05.2014 14:19, schrieb David Kastrup:
> Urs Liska <address@hidden> writes:
>
> > Hi,
> >
> > I have this construct in a function that creates a combined time signature:
> >
> >     (grob-interpret-markup grob
> >       (markup #:override '(baseline-skip . 0) #:number
> >         (#:line ((#:column (numOne denOne))
> >                  (#:column (numTwo denTwo))))))
> >
> > It creates two columns from the four given arguments, but I want to be
> > able to create an arbitrary number of columns.
> >
> > I see that #:line gets a list of (#:column ()) entries.
> > But I'm lost with the #: part. What does that mean?
>
> That's the markup macro.  It is documented in the Extending Guide.  More
> or less.
>
> > And how can I generate such a list with an arbitrary number of
> > columns?
>
> You can't actually do it in time since the whole point of a macro is
> that it operates on its elements _before_ they are evaluated.
>
> So the Extending Guide says:
>
> Known issues and warnings
> .........................
>
> The markup-list argument of commands such as ‘#:line’, ‘#:center’, and
> ‘#:column’ cannot be a variable or the result of a function call.
>
>       (markup #:line (function-that-returns-markups))
>
> is invalid.  One should use the ‘make-line-markup’,
> ‘make-center-markup’, or ‘make-column-markup’ functions instead,
>
>       (markup (make-line-markup (function-that-returns-markups)))

That's how far I got - after writing the email ...

> So let's fiddle this in another way:
That's where I did _not_ get

> Of course, we can just abandon hope regarding the markup macro and do
> this as

and this neither.
But I could incorporate the second solution in my function, and now it's 
a neat \alternatingTimeSignatures function.

Compile the attached file to see it in action.
I think this should be generally available, and if you don't think it 
should be included in LilyPond I'll put it in the openLilyLib snippets.

Best
Urs

alternatingTimeSignatures.ly
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