Re: TimeSignature with note in denominator

[David Kastrup]

Carl Sorensen <c_sorensen@byu.edu> writes:

> On 11/15/21, 10:21 AM, "lilypond-devel on behalf of Flaming Hakama by 
> Elaine" <lilypond-devel-bounces+carl.d.sorensen+digest=gmail.com@gnu.org on 
> behalf of elaine@flaminghakama.com> wrote:
>
>     
>     According to the semantics quoted several times, the denominator describes
>     the length/duration of the unit, the numerator describes how many units 
> are
>     in the measure.
>
> There is some space for confusion in the LilyPond world.  Moments represent a 
> musical moment, an instant in time.  But a moment is also used to represent a 
> time interval between the current moment and the zero moment (such as the 
> beginning of  a measure).  So a moment also can be used to represent an 
> interval, as is applied in the time signature.  I should have been more 
> sensitive to this, because I created the BaseMoment property to be used in 
> autobeaming; this property represents and interval starting at 0 and ending 
> at the moment BaseMoment.
>     
>     In terms of semantics, numerals and note representation operate exactly 
> the
>     same.  There is  a 1-1 mapping between numbers interpreted as fractions of
>     a whole note, and the graphical symbols used to represent those
>     durations/lengths.

That is simply untrue.

\tuplet 2/3 { 4 } and 4. are different graphical symbols representing
exactly the same length.  Similarly \tuplet 3/2 ... and \tuplet 6/4
... represent the exactly the same length but have different graphical
representations, note durations and musical semantics.

Claiming that there is a 1-1 mapping and that one can exchange on for
the other in the internals without consequences is just not going to
help.

And there is a huge tendency here to conflate that the existence of an
n->1 mapping for durations/graphics to a moment length with the
existence of a 1-1 mapping and to build lots of strawmen based on
claiming I deny the existence of the n->1 mapping and "proving" in that
manner that I don't know what I am talking about.

> Now, music expressions also have a length, even if they don't have a
> lilypond duration.  And it is possible to get the length of a music
> expression and return it as a Moment using ly:music-length.  So if it
> were possible to have the parser (or a music function) take two
> arguments for a time signature, with the first being an integer and
> the second being a music expression, it would be relatively
> straightforward to convert this into a reasonable time signature.

Where "convert this into a reasonable time signature" would imply the
ability to convert this into the two separate components, a functional
and a visual one.  At the current point of time, something like
2/4. (for what is commonly referred to as 6/8 in standard notation) has
no natural conversion to the functional components
numerator/denominator.  One could do this "more naturally" by allowing
the "denominator" to be a rational number instead of just an integer.

The _visual_ component still needs a separate expression that probably
sticks best with being actual music once one puts out note images.  That
would allow for example a meter of 4 times \tuplet 3/2 { 4 8 } for some
weird swing time indication, or 3 times { 8 8 8 } for a different
representation of 9/8 meter.

With regard to meters, obviously there are also numeric variations like
writing 3+2 in the numerator.  The amount of visual possibilities is
large enough that forcing visual and functional components to be
interchangeable seems like a bad idea.

-- 
David Kastrup