Extending LilyPond: 2.1.5 Functions without arguments

### 2.1.5 Functions without arguments

In most cases a function without arguments should be written with a variable,

>     dolce = \markup{ \italic \bold dolce }

However, in rare cases it may be useful to create a music function without arguments,

>     displayBarNum =
>     #(define-music-function
>          (parser location)
>          ()
>        (if (eq? #t (ly:get-option 'display-bar-numbers))
>            #{ \once \override Score.BarNumber #'break-visibility = ##f #}
>            #{#}))

To actually display bar numbers where this function is called, invoke `lilypond` with

>     lilypond -d display-bar-numbers FILENAME.ly

其它语言：deutsch, español。

#### LilyPond — Extending