Doc: simplify example for unpure-pure containers

Doc: simplify example for unpure-pure containers

Use of ly:event-property only confuses matters.  Squares are never used.

Draw circles unconditionally, make them empty inside (which would make
the wrong output easier to discern) and name the macros roundNotes and
smartRoundNotes.  No need to define a separate Scheme function, a
one-line lambda in stencil definition is enough.

Don't remove Stem_engraver, just use whole notes and adjust the time
signature.

[Pavel Roskin, 2012-02-02 19:32:50]

The example could be much simpler and still show the problem being addressed by
the unpure-pure containers.

[Graham Percival, 2012-02-02 21:14:02]

LGTM, but I'd like David or Mike to give it the ok.  If they do, I think this
can be pushed directly.

[Pavel Roskin, 2012-02-03 15:38:16]

To be honest, there are many things I don't understand.  In fact, I reduced the
example to understand it better.

Why is horizontal spacing affected even though the purity affects the Y-axis
only?  Why do stems fix the spacing?  Why doesn't this cause the spacing
problem:

  \override NoteHead #'text = \markup { "o" }
  \override NoteHead #'stencil = #ly:text-interface::print

But this does cause the problem:

  \override NoteHead #'text = \markup { "o" }
  \override NoteHead #'stencil =
   #(lambda (grob) (ly:text-interface::print grob))

Cannot it happen a simple change would make Lilypond recognize lambda
expressions as pure functions, breaking this example?  Maybe I removed some
future-proofing?

Perhaps some answers to those questions could be used to improve the
documentation.

[Pavel Roskin, 2012-03-02 23:59:13]

Since nobody is interested, I'm closing this issue.

[dak, 2012-03-03 05:37:40]

On 2012/02/03 15:38:16, Pavel Roskin wrote:
> To be honest, there are many things I don't understand.  In fact, I reduced
the
> example to understand it better.
> 
> Why is horizontal spacing affected even though the purity affects the Y-axis
> only?  Why do stems fix the spacing?  Why doesn't this cause the spacing
> problem:
> 
>   \override NoteHead #'text = \markup { "o" }
>   \override NoteHead #'stencil = #ly:text-interface::print
> 
> But this does cause the problem:
> 
>   \override NoteHead #'text = \markup { "o" }
>   \override NoteHead #'stencil =
>    #(lambda (grob) (ly:text-interface::print grob))
> 
> Cannot it happen a simple change would make Lilypond recognize lambda
> expressions as pure functions, breaking this example?  Maybe I removed some
> future-proofing?
> 
> Perhaps some answers to those questions could be used to improve the
> documentation.

See the end of define-grobs.scm.  purity detection is hardwired.

[mike_apollinemike.com, 2012-03-03 06:58:09]

On Feb 3, 2012, at 4:38 PM, plroskin@gmail.com wrote:

> To be honest, there are many things I don't understand.  In fact, I
> reduced the example to understand it better.
> 
> Why is horizontal spacing affected even though the purity affects the
> Y-axis only?

Because horizontal spacing is based on thing's height.  If something is tall, it
may lead to wider spacing as it cannot be kerned.

> Why do stems fix the spacing?

I don't understand the question :(

> Why doesn't this cause the
> spacing problem:
> 
>  \override NoteHead #'text = \markup { "o" }
>  \override NoteHead #'stencil = #ly:text-interface::print
> 

text-interface::print is declared pure towards the bottom of define-grobs.scm

> But this does cause the problem:
> 
>  \override NoteHead #'text = \markup { "o" }
>  \override NoteHead #'stencil =
>   #(lambda (grob) (ly:text-interface::print grob))
> 
> Cannot it happen a simple change would make Lilypond recognize lambda
> expressions as pure functions, breaking this example?

This is why unpure-pure-containers exist.

Cheers,
MS

[c_sorensen, 2012-03-03 14:33:27]

On 3/2/12 11:58 PM, "mike@apollinemike.com" <mike@apollinemike.com> wrote:

>On Feb 3, 2012, at 4:38 PM, plroskin@gmail.com wrote:
>
>> Why do stems fix the spacing?
>
>I don't understand the question :(

I believe it's because stems are involved in optical spacing decisions.

Thanks,

Carl

[Pavel Roskin, 2012-03-03 17:19:41]

I mean, why is this needed?
\remove "Stem_engraver"
Stems must be fixing the problem somehow.