Re: Proposed context property renaming

[Saul Tobin]

Regarding length vs. moment, David's comment from the previous thread on
this topic may shed some light:
https://mail.gnu.org/archive/html/lilypond-devel/2024-10/msg00017.html

On Thu, Dec 12, 2024 at 11:16 AM Trevor Bača <trevorbaca@gmail.com> wrote:

> On Wed, Dec 11, 2024 at 4:32 PM Dan Eble <nine.fierce.ballads@gmail.com>
> wrote:
>
> > On 2024-12-11 14:04, Trevor Bača wrote:
> >  >
> > > Thinking this way, proportionalNotationDuration is named correctly,
> > because
> > > what's being set here is a unit of time.
> >  >
> >
> > I am not sure that I made my reason for wanting to rename this clear.
> > Maybe this will help:
> >
> > ```
> > \version "2.24.0"
> >
> > {
> >    \set Score.voltaSpannerDuration = #(ly:make-moment 1/4)
> >    \applyContext
> >    #(lambda (ctx)
> >      (let ((duration (ly:context-property ctx 'voltaSpannerDuration #f)))
> >       (if (ly:duration? duration)
> >        (display (format #f "\nvoltaSpannerDuration is ~a\n" duration))
> >        (display "\nhuh... I guess voltaSpannerDuration isn't a
> > duration\n"))))
> >
> >    s1
> > }
> > ```
> >
> > The "huh..." message appears in the output.
> >
>
> Ah, so voltaSpannerDuration accepts only whatever the output type of
> make-moment is? A moment?
>
> And the snippet above shows that ly:duration? returns false when evaluated
> on a LilyPond moment?
>
> So, yes, I see the discordance between "moment" and "duration". But see
> more, below.
>
>
>
> > > Regardless of the names of Lily's underlying (and therefore
> > > user-invisible?) types, these user-facing context properties all
> measure
> > > time, and not space. I think there might be a real gain in clarity in
> the
> > > public-facing API if we move to labeling time-based properties with
> > > "duration" and reserve "length" for properties that measure things in
> > > centimeters, inches, staff spaces and the like.
> >
> >      { c4 }
> >      \set Score.voltaSpannerDuration = #1/4
> >
> > Both of these numbers refer to the musical length of a quarter note.
> > (The "4" on the note also has other attributes.)  Are both of them
> > durations, or is one the duration and the other the reciprocal of the
> > duration?  How would you explain the difference to the kind of user you
> > have in mind (who does not care about internal types)?
>
>
> > The Notation Reference has explained this special definition of
> > "duration" is for quite some time:
> >
> >      Durations
> >
> >      The durations of notes are entered using numbers and dots.
> >      The number entered is based on the reciprocal value of the
> >      length of the note.
> >
> > In my view, if jargon like this must be defined, it should be used
> > carefully and consistently.  That is why I support renaming the
> > properties that have been using "duration" in a broader sense.
> >
>
> I was with you until the very last sentence.
>
> Isn't it the case that ...
>
>      { c4 }
>      \set Score.voltaSpannerDuration = #1/4
>
> ... are two ways of referring to the same thing: a unit of time equal to
> one quarter of a whole note? Two different types being used to model the
> same thing, correct?
>
> So, at least from a type-unaware perspective, voltaSpannerDuration is named
> correctly, yes?
>
> But I understand the discordance that happens when we become of the types
> that are being passed around: voltaSpannerDuration wants a moment as a
> type, even though voltaSpannerDuration is modeling a duration.
>
> Question: if what we're wanting is to harmonize according to the types that
> are being passed around (which, to be clear, is not what I think should
> happen in public-facing parts of the API), then why not rename
> voltaSpannerDuration to voltaSpannerMoment instead of
> voltaSpannerMusicLength? In other words, what's the motivation for further
> spreading around musicLength when the underlying type is presumably Moment?
>
> Trevor.
>
>
> --
> Trevor Bača
> www.trevorbaca.com
> soundcloud.com/trevorbaca
>