2.1 LilyPond code blocks (Extending LilyPond)

### 2.1 LilyPond code blocks

Creating music expressions in Scheme can be tedious, as they are heavily nested and the resulting Scheme code is large. For some simple tasks this can be avoided by using LilyPond code blocks, which enable common LilyPond syntax to be used within Scheme.

LilyPond code blocks look like

    #{ LilyPond code #}

Here is a trivial example:

>     ritpp = #(define-event-function () ()
>       #{ ^"rit." \pp #}
>     )

>     { c'4 e'4\ritpp g'2 }

LilyPond code blocks can be used anywhere where you can write Scheme code. The Scheme reader actually is changed for accommodating LilyPond code blocks and can deal with embedded Scheme expressions starting with ‘`$`’ and ‘`#`’.

The reader extracts the LilyPond code block and generates a runtime call to the LilyPond parser to interpret the LilyPond code. Scheme expressions embedded in the LilyPond code are evaluated in the lexical environment of the LilyPond code block, so all local variables and function parameters available at the point the LilyPond code block is written may be accessed. Variables defined in other Scheme modules, like the modules containing `\header` and `\layout` blocks, are not accessible as Scheme variables, i.e., prefixed with ‘`#`’, but they are accessible as LilyPond variables, i.e., prefixed with ‘`\`’.

All music generated inside the code block has its ‘`origin`’ set to the current input location.

A LilyPond code block may contain anything that you can use on the right side of an assignment. In addition, an empty LilyPond block corresponds to a void music expression, and a LilyPond block containing multiple music events gets turned into a sequential music expression.

#### Extending LilyPond v2.26.0 (stable-branch).

- 1 Scheme tutorial
  - 1.1 Introduction to Scheme
    - 1.1.1 Scheme sandbox
    - 1.1.2 Scheme variables
    - 1.1.3 Scheme simple data types
    - 1.1.4 Scheme compound data types
      - Pairs
      - Lists
      - Association lists (alists)
      - Hash tables
    - 1.1.5 Calculations in Scheme
    - 1.1.6 Scheme procedures
      - Defining procedures
      - Predicates
      - Return values
    - 1.1.7 Scheme conditionals
      - if
      - cond
  - 1.2 Scheme in LilyPond
    - 1.2.1 LilyPond Scheme syntax
    - 1.2.2 LilyPond variables
    - 1.2.3 Debugging Scheme code
    - 1.2.4 Input variables and Scheme
    - 1.2.5 Importing Scheme in LilyPond
    - 1.2.6 Object properties
    - 1.2.7 LilyPond compound variables
      - Offsets
      - Fractions
      - Extents
      - Property alists
      - Alist chains
    - 1.2.8 LilyPond’s box model
    - 1.2.9 Internal music representation
  - 1.3 Building complicated functions
    - 1.3.1 A first approach (example)
    - 1.3.2 Displaying music expressions
    - 1.3.3 Music properties
    - 1.3.4 Doubling a note with slurs (example)
    - 1.3.5 Adding articulation to notes (example)
- 2 Interfaces for programmers
  - 2.1 LilyPond code blocks
  - 2.2 Scheme functions
    - 2.2.1 Scheme function definitions
    - 2.2.2 Scheme function usage
    - 2.2.3 Void Scheme functions
  - 2.3 Music functions
    - 2.3.1 Music function definitions
    - 2.3.2 Music function usage
    - 2.3.3 Simple substitution functions
    - 2.3.4 Intermediate substitution functions
    - 2.3.5 Mathematics in functions
    - 2.3.6 Functions without arguments
    - 2.3.7 Void music functions
  - 2.4 Event functions
  - 2.5 Markup functions
    - 2.5.1 Markup construction in Scheme
    - 2.5.2 How markups work internally
    - 2.5.3 New markup command definition
      - Markup command definition syntax
      - On properties
      - A complete example
      - Adapting builtin commands
      - Converting markups to strings
    - 2.5.4 New markup list command definition
  - 2.6 Contexts for programmers
    - 2.6.1 Context evaluation
    - 2.6.2 Running a function on all layout objects
  - 2.7 Callback functions
  - 2.8 Unpure-pure containers
  - 2.9 Difficult tweaks
- 3 LilyPond Scheme interfaces
- Appendix A GNU Free Documentation License
- Appendix B Index