### 3.4.4 Saving typing with variables and functions

By this point, you’ve seen this kind of thing:

>     hornNotes = \relative c'' { c4 b dis c }

>     \score {
>       {
>         \hornNotes
>       }
>     }

You may even realize that this could be useful in minimalist music:

>     fragmentA = \relative c'' { a4 a8. b16 }
>     fragmentB = \relative c'' { a8. gis16 ees4 }

>     violin = \new Staff {
>       \fragmentA \fragmentA |
>       \fragmentB \fragmentA |
>     }

>     \score {
>       {
>         \violin
>       }
>     }

However, you can also use these variables (also known as macros, or user-defined commands) for tweaks:

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

>     padText = { \once \override TextScript.padding = #5.0 }
>     fthenp =_\markup {
>       \dynamic f \italic \small { 2nd } \hspace #0.1 \dynamic p
>     }

>     violin = \relative c'' {
>       \repeat volta 2 {
>         c4._\dolce b8 a8 g a b |
>         \padText
>         c4.^"hi there!" d8 e' f g d |
>         c,4.\fthenp b8 c4 c-. |
>       }
>     }

>     \score {
>       {
>         \violin
>       }
>       \layout { ragged-right = ##t }
>     }

These variables are obviously useful for saving typing. But they’re worth considering even if you only use them once – they reduce complexity. Let’s look at the previous example without any variables. It’s a lot harder to read, especially the last line.

>     violin = \relative c'' {
>       \repeat volta 2 {
>         c4._\markup { \italic \bold dolce } b8 a8 g a b |
>         \once \override TextScript.padding = #5.0
>         c4.^"hi there!" d8 e' f g d |
>         c,4.\markup {
>           \dynamic f \italic \small { 2nd } \hspace #0.1 \dynamic p
>         }
>         b8 c4 c-. |
>       }
>     }

So far we’ve seen static substitution – when LilyPond sees `\padText`, it replaces it with the stuff that we’ve defined it to be (ie the stuff to the right of `padtext=`).

LilyPond can handle non-static substitution, too (you can think of these as functions).

>     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 |
>     }

Using variables is also a good way to reduce work if the LilyPond input syntax changes (see Updating files with convert-ly). If you have a single definition (such as `\dolce`) for all your input files (see Style sheets), then if the syntax changes, you only need to update your single `\dolce` definition, instead of making changes throughout every ‘`.ly`’ file.

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#### LilyPond — Learning Manual v2.18.2 (稳定分支).