define-*.scm

[Nicolas Sceaux]

Hello,

I was wondering if some syntax could be added in the scm/define-**.scm
files. For instance, a user may want to define a new music property,
to be used in a music function. I once had to do:

  %% We add a `not-tuplefiable' music property
  #(let ((my-prop 'not-tuplefiable))
    (set-object-property! my-prop 'music-type? boolean?)
    (set-object-property! my-prop 'music-doc "Set to #t if the sequence should 
not be tuplefied by \\tuplefy")
    (set! all-music-properties (cons my-prop all-music-properties)))

It would have been easier to do, eg:

  #(define-music-property not-tuplefiable boolean?
     "Set to #t if the sequence should not be tuplefied by \\tuplefy")

I suspect that define-music-properties.scm might also benefit from
that, by not using backquotes, unquotes, etc.

(define-all-music-properties
  (iterator-ctor   procedure?   "Function to construct music-event-iterator 
object for this Music")
  (duration        ly:duration? "Duration of this note/lyric.")
  (metronome-count number?      "How many beats in a minute?"))

This may be more obvious with scm/define-grobs.scm. There would be:

(define-grob-description Arpeggio (arpeggio-interface 
staff-symbol-referencer-interface side-position-interface item-interface 
font-interface)
  (X-extent-callback  Arpeggio::width_callback)
  (Y-extent-callback  #f)       
  (print-function     Arpeggio::print)
  (Y-offset-callbacks (list Staff_symbol_referencer::callback))
  (X-offset-callbacks (list Side_position_interface::aligned_side))
  (direction          -1)
  (padding            0.5)
  (staff-position     0.0))

(define-grob-description TextSpanner (text-spanner-interface 
side-position-interface font-interface spanner-interface)
  (print-function Text_spanner::print)
  (font-shape     'talic)
  (style          'dashed-line)
  (staff-padding  0.1)
  (dash-fraction  0.2)
  (dash-period    3.0)
  (direction      1))
...

And a(n advanced) user could do, to override a bunch of grob
properties in eg an init file:

(custom-grob-descriptions
  (Arpeggio padding 1.0)
  (TextSpanner staff-padding 0.8)
  ;; ...
  )

scm/define-music-types.scm could become:

(define-music-type MultiMeasureRestMusicGroup "Music" (general-music 
sequential-music)
  "Like sequential-music, but specifically intended
to group start-mmrest, skip, stop-mmrest sequence. 

Syntax @code{R2.*5} for 5 measures in 3/4 time."
  (length-callback Music_sequence::cumulative_length_callback)
  (start-callback  Music_sequence::first_start_callback)
  (iterator-ctor   Sequential_music_iterator::constructor))

(define-music-type AutoChangeMusic "Music_wrapper" (general-music 
music-wrapper-music auto-change-instruction)
  "Used for making voices that switch between piano staves automatically."
  (iterator-ctor   Auto_change_iterator::constructor))

(define-music-type SoloOneEvent "Event" (general-music event part-combine-event)
  "Print Solo.1"
  (part-combine-status 'solo1))

...

In scm/define-grobs.scm, we read:

;;;; WARNING: the meta field should be the last one.
;;;; WARNING: don't use anonymous functions for initialization.

;; TODO: junk the meta field in favor of something more compact?

Using define-grob-description, we could take care of that.

nicolas