Re: Catch direction operators

[David Kastrup]

Thomas Morley <address@hidden> writes:

>>>>You can write:
>>>>colorizeDir =
>>>>#(define-music-function (parser location item)
>>>>   (symbol-list-or-music?)
>>>>   (define (grob-colorize-dir grob)
>>>>     (let ((ev (event-cause grob)))
>>>>       (case (ly:event-property ev 'direction)
>>>>             ((1) red)
>>>>             ((-1) blue)
>>>>             (else '()))))
>>>>   #{ \tweak color #grob-colorize-dir #item #})
>>>
>>> Thanks, this works perfectly.
>>>
>>> I would like to add this to a Frescobaldi addition and later (once
>>> 2.18 is out) to a LilyPond addition proposal. Do you have any
>>> objections?
>>
>> You can add it wherever you want.  I don't see it making any sense as an
>> addition to LilyPond proper as it is a rather special use case.  It may
>> still be nice as a snippet as it is simple, flexible, and powerful.  The
>> use cases also show \tweak as an internal workhorse for both tweaks and
>> overrides.
>>
>> As a snippet, it makes sense _in_ 2.18 as it illustrates current
>> programming techniques.
>
> I thought it would be nice to apply such a function to not only one
> grob, but rather a list of grobs or all possible grobs.
> Though, I didn't manage to generalize David K's tweak-function.

Here is a generalization:

colorizeDir =
#(define-music-function (parser location item)
   (symbol-list-or-music?)
   (define (grob-colorize-dir grob)
     (let ((ev (event-cause grob)))
       (case (ly:event-property ev 'direction)
             ((1) red)
             ((-1) blue)
             (else '()))))
   #{ \tweak color #grob-colorize-dir #item #})

mapList =
#(define-music-function (parser location fun lst)
  (ly:music-function? list?)
  #{ $@(map (lambda (s) #{ $fun $s #}) lst) #})

\new Voice \with { \mapList #colorizeDir Slur.StringNumber.TextScript }
{
    a4-( b)
    a4^( b)
    a''4_( b)

    c''-3\4-"xy"
    c''_3^\4^"xy"
    c''^3_\4_"xy"
}


-- 
David Kastrup