Extending LilyPond: 2.2.1 Markup construction in Scheme

### 2.2.1 Markup construction in Scheme

The `markup` macro builds markup expressions in Scheme while providing a LilyPond-like syntax. For example,

>     (markup #:column (#:line (#:bold #:italic "hello" #:raise 0.4 "world")
>                       #:larger #:line ("foo" "bar" "baz")))

is equivalent to:

>     \markup \column { \line { \bold \italic "hello" \raise #0.4 "world" }
>                       \larger \line { foo bar baz } }

This example demonstrates the main translation rules between regular LilyPond markup syntax and Scheme markup syntax.

> LilyPond | Scheme
> `\markup markup1` | `(markup markup1)`
> `\markup { markup1 markup2 ... }` | `(markup markup1 markup2 ... )`
> `\markup-command` | `#:markup-command`
> `\variable` | `variable`
> `\center-column { ... }` | `#:center-column ( ... )`
> `string` | `"string"`
> `#scheme-arg` | `scheme-arg`

The whole Scheme language is accessible inside the `markup` macro. For example, You may use function calls inside `markup` in order to manipulate character strings. This is useful when defining new markup commands (see New markup command definition).

#### Known issues and warnings

The markup-list argument of commands such as `#:line`, `#:center`, and `#:column` cannot be a variable or the result of a function call.

    (markup #:line (function-that-returns-markups))

is invalid. One should use the `make-line-markup`, `make-center-markup`, or `make-column-markup` functions instead,

    (markup (make-line-markup (function-that-returns-markups)))

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#### LilyPond — Extending