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5.6.1 Substitution function syntax
Making a function that substitutes a variable into LilyPond code is easy. The general form of these functions is
function = #(define-music-function (parser location arg1 arg2 …) (type1? type2? …) #{ …music… #})
where
argN | nth argument |
typeN? | a scheme type predicate for which argN
must return #t . |
…music… | normal LilyPond input, using $ (in places where only
Lilypond constructs are allowed) or # (to use it as a Scheme
value or music function argument or music inside of music lists) to
reference arguments
(eg. ‘#arg1’). |
The parser
and location
arguments are mandatory, and
are used in some advanced situations as described in the
‘Extending’ manual (see
Music functions). For
substitution functions, just be sure to include them.
The list of type predicates is also required. Some of the most common type predicates used in music functions are:
boolean? cheap-list? (use instead of ‘list?’ for faster processing) ly:duration? ly:music? ly:pitch? markup? number? pair? string? symbol?
For a list of available type predicates, see Predefined type predicates. User-defined type predicates are also allowed.
See also
Notation Reference: Predefined type predicates.
Extending Lilypond: Music functions.
Installed Files: ‘lily/music-scheme.cc’, ‘scm/c++.scm’, ‘scm/lily.scm’.
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