Re: how to define a boolean?

[Carl Sorensen]

On 8/10/09 1:54 AM, "Marc Hohl" <address@hidden> wrote:

> Carl Sorensen schrieb:
>> [...]
>> 
>> The *specific* behavior you have requested can be achieved by the following:
>> 
>> #(define myBool #f)
>> 
>> myMusicFunc =
>> #(define-music-function (parser location) ()
>>    #{
>>      \once \override Slur #'dummyProperty = ##t
>>    #})
>> 
>> #(define-public (slur::boolean grob)
>>   ;; just a test function to try and switch boolean values
>>     (let ((my-prop (ly:grob-property grob 'dummyProperty #f)))
>>       (display "\nWithin callback\n")
>>       (display "my-prop: ")(display my-prop)(newline)
>>     (if my-prop
>>         (display "Actions for #t go here...")
>>         (display "Actions for #f go here..."))
>>     (set! myBool #f)
>>     (display "myBool: ")(display myBool)(newline)
>>     (ly:slur::print grob)))
>> 
>> \layout {
>>   \context {
>>     \Voice
>>     \override Slur #'stencil = #slur::boolean
>>   }
>> }
>> 
>> \relative c'' {
>>     c4 ( c )
>>     \myMusicFunc
>>     c ( c )
>>     c ( c )
>>     \myMusicFunc
>>     c ( c )
>> }
>> 
>>  
> Ok, I played with your code - the result on console for my-prop is #f #t
> #t #f,
> but it should be #f #t #f #t, isn't it?

Hmm, you're right.

I did a little bit of extra investigating, including adding the following to
slur::boolean

      (display "cause: ")(display (event-cause grob))(newline)

When I did this, I found that the first #f came from the first line of
music, the first #t came from the second line of music, the second  #t came
from the *last* line of music, and the second #f came from the third line of
music.  Somehow the connected slurs changed the order of evaluation, but the
slurs that I expected to have the property #t did in fact have the property
#t.

If I add an extra note to each line of music, so the slurs aren't connected,
then I get #f #t #f #t as expected.

I have answered *what* is happening to my satisfaction.  But I really don't
know *why*.  This question goes beyond my understanding of LilyPond.
Perhaps asking on -devel would get an answer from somebody who understands
more than I do.

Thanks,

Carl