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Re: TimeSignature with note in denominator

From: David Kastrup
Subject: Re: TimeSignature with note in denominator
Date: Sun, 14 Nov 2021 08:59:28 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux)

Kieren MacMillan <> writes:

> Hi David,
>> No.  You propose replacing (cons 3 4) as a time signature designation
>> with (cons 3 (ly:make-duration 2)).  You have failed to give any
>> indication of what you want to see (cons 8 20) replaced with.
> Well at least now you’ve asked the question you clearly meant to ask
> earlier, in a way that someone other than you can figure out how to
> answer in the way you’re expecting.  =)
>> It will likely end up as (ly:make-duration 4 0 4/5)
> That seems fine to me.
>> but that has no unique printed representation different from 
>> (ly:make-duration 4)
> Correction: Lilypond doesn’t, by default, give a “unique printed
> representation” to (ly:make-duration 4 0 4/5) as compared with
> (ly:make-duration 4). On the other hand, I am fully capable of making
> Lilypond do so, i.e., formatting the denominator as a sixteenth note
> *with a '5' [possibly in a bracket] below it*, which absolutely *is* a
> “unique printed representation”, and will convey to the performer
> exactly the desired meaning.
>> (ly:make-duration 4 0 4/5) and (ly:make-duration 4 0 8/10)
>> are absolutely indistinguishable.
> I can do the math to back-calc either of those into a note duration in
> order to determine.

There is no either of those.  They are identical.  You cannot
distinguish a 5-tuplet from a 10-tuplet in that representation.

> So I guess here’s my [final] answer to your question: I’d like to see
> (cons 8 20) replaced with whatever is easiest for the lexer / parser
> to convert to and from and/or pass through to the time function(s)
> without losing any critical information about the denominator
> duration.

You are just evading the question.  The problem is that there is no
unique representation as a LilyPond duration for print forms
representing 1/20th of a whole note, and you and Carl are glossing over
the fact that the time signature 8/20 does not actually specify such a
duration but does, contrary to your theories, indicates 1/20 of a whole
note as the unit without specifying _how_ this unit is actually
musically established in terms of durations.

> Feel free to ask me for yet another answer to this question… but be
> warned that I don’t know enough about the lexer or parser or
> Lilypond’s internal representation of durations to give a more
> specific or nuanced or helpful answer than that.  ;)

The problem is that handwaving looks great in discussions but does not
deliver a definition useful for implementation.

David Kastrup

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