5.6 Advanced tweaks with Scheme

We have seen how LilyPond output can be heavily modified using commands like \override TextScript #'extra-offset = ( 1 . -1). But we have even more power if we use Scheme. For a full explantion of this, see the Scheme tutorial and Interfaces for programmers.

We can use Scheme to simply \override commands,

     
     padText = #(define-music-function (parser location padding) (number?)
     #{
       \once \override TextScript #'padding = #$padding
     #})
     
     \relative c''' {
       c4^"piu mosso" b a b
       \padText #1.8
       c4^"piu mosso" d e f
       \padText #2.6
       c4^"piu mosso" fis a g
     }

We can use it to create new commands,

     
     tempoMark = #(define-music-function (parser location padding marktext)
                                         (number? string?)
     #{
       \once \override Score . RehearsalMark #'padding = $padding
       \once \override Score . RehearsalMark #'no-spacing-rods = ##t
       \mark \markup { \bold $marktext }
     #})
     
     \relative c'' {
       c2 e
       \tempoMark #3.0 #"Allegro"
       g c
     }

Even music expressions can be passed in.

     
     pattern = #(define-music-function (parser location x y) (ly:music? ly:music?)
     #{
       $x e8 a b $y b a e
     #})
     
     \relative c''{
       \pattern c8 c8\f
       \pattern {d16 dis} { ais16-> b\p }
     }