+@c -*-texinfo-*-
@node Interfaces for programmers
@appendix Interfaces for programmers
@menu
* Programmer interfaces for input ::
-* Markup programmer interface::
-* Contexts for programmers::
+* Markup programmer interface::
+* Contexts for programmers::
@end menu
@node Programmer interfaces for input
@appendixsec Programmer interfaces for input
@menu
-* Input variables and Scheme::
+* Input variables and Scheme::
* Internal music representation::
-* Manipulating music expressions::
+* Extending music syntax::
+* Manipulating music expressions::
+* Using LilyPond syntax inside Scheme::
@end menu
@node Input variables and Scheme
\score @{ #(ly:export (make-sequential-music newLa)) @}
@end example
+@refbugs
+
+Mixing Scheme and lily identifiers is not possible with @code{--safe}.
@node Internal music representation
@appendixsubsec Internal music representation
@item
`type' or interface: Each music name has several `types' or interface,
- for example, a note is an @code{event}, but it is also a @code{note-event},
- a @code{rhythmic-event} and a @code{melodic-event}.
+ for example, a note is an @code{event},
+ but it is also a @code{note-event},
+ a @code{rhythmic-event} and
+ a @code{melodic-event}.
All classes of music are listed in the internals manual, under
@internalsref{Music classes}.
@code{element}. The body of a repeat is in @code{element} property of
@internalsref{RepeatedMusic}, and the alternatives in @code{elements}.
+
+
+
+@node Extending music syntax
+@appendixsubsec Extending music syntax
+
+The syntax of composite music expressions, like
+@code{\repeat}, @code{\transpose} and @code{\context}
+follows the general form of
+
+@example
+ \@code{keyword} @var{non-music-arguments} @var{music-arguments}
+@end example
+
+Such syntax can also be defined as user code. To do this, it is
+necessary to create a @emph{music function}. This is a specially marked
+Scheme function. For example, the music function @code{\applymusic} applies
+a user-defined function to a music expression. Its syntax is
+
+@example
+\applymusic #@var{func} @var{music}
+@end example
+
+A music function is created with @code{ly:make-music-function},
+
+@example
+ (ly:make-music-function
+@end example
+
+@code{\applymusic} takes a Scheme function and a Music expression as
+argument. This is encoded in its first argument,
+
+@example
+ (list procedure? ly:music?)
+@end example
+
+The function itself takes another argument, an Input location
+object. That object is used to provide error messages with file names
+and line numbers. The definition is the second argument of
+@code{ly:make-music-function}. The body is function simply calls the
+function
+
+@example
+ (lambda (where func music)
+ (func music))
+@end example
+
+The above Scheme code only defines the functionality. The tag
+@code{\applymusic} is selected by defining
+
+@example
+ applymusic = #(ly:make-music-function
+ (list procedure? ly:music?)
+ (lambda (location func music)
+ (func music)))
+@end example
+
+A @code{def-music-function} macro is introduced on top of
+@code{ly:make-music-function} to ease the definition of music
+functions:
+
+@example
+ applymusic = #(def-music-function (location func music) (procedure? ly:music?)
+ (func music))
+@end example
+
+Examples of the use of @code{\applymusic} are in the next section.
+
+@seealso
+@file{ly/music-functions-init.ly}.
+
@node Manipulating music expressions
@appendixsubsec Manipulating music expressions
Music objects and their properties can be accessed and manipulated
-directly, through the @code{\apply} mechanism.
-The syntax for @code{\apply} is
+directly, through the @code{\applymusic} mechanism.
+The syntax for @code{\applymusic} is
@example
-\apply #@var{func} @var{music}
+\applymusic #@var{func} @var{music}
@end example
@noindent
(ly:music-set-property! m 'elements (reverse
(ly:music-property m 'elements)))
m)
- \score { \notes \apply #rev-music-1 { c4 d4 } }
+ \score { \notes \applymusic #rev-music-1 { c4 d4 } }
@end lilypond
The use of such a function is very limited. The effect of this
multiple children. The following function application has no effect:
@example
- \apply #rev-music-1 \grace @{ c4 d4 @}
+ \applymusic #rev-music-1 \grace @{ c4 d4 @}
@end example
@noindent
In this case, @code{\grace} is stored as @internalsref{GraceMusic}, which has no
@code{elements}, only a single @code{element}. Every generally
-applicable function for @code{\apply} must -- like music expressions
+applicable function for @code{\applymusic} must -- like music expressions
themselves -- be recursive.
The following example is such a recursive function: It first extracts
\context Voice = "2" @{ \voiceTwo b @} >>
@end example
-Other applications of @code{\apply} are writing out repeats
+Other applications of @code{\applymusic} are writing out repeats
automatically (@inputfileref{input/test,unfold-all-repeats.ly}),
saving keystrokes (@inputfileref{input/test,music-box.ly}) and
exporting
@inputfileref{input/test,music-box.ly}.
+@node Using LilyPond syntax inside Scheme
+@appendixsubsec Using LilyPond syntax inside Scheme
+
+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, using LilyPond usual syntax inside
+scheme, with the dedicated @code{#@{ ... #@}} syntax.
+
+The following two expressions give equivalent music expressions:
+@example
+ mynotes = @{ \override Stem #'thickness = #4
+ \notes @{ c'8 d' @} @}
+
+ #(define mynotes #@{ \override Stem #'thickness = #4
+ \notes @{ c'8 d' @} #@})
+@end example
+
+The content of @code{#@{ ... #@}} is enclosed in an implicit @code{@{
+... @}} block, which is parsed. The resulting music expression, a
+@code{SequentialMusic} music object, is then returned and usable in scheme.
+
+Arbitrary scheme forms, including variables, can be used in @code{#@{ ... #@}}
+expressions with the @code{$} character (@code{$$} can be used to
+produce a single $ character). This makes the creation of simple
+functions straightforward. In the following example, a function
+setting the TextScript's padding is defined:
+
+@lilypond[verbatim,raggedright]
+ #(use-modules (ice-9 optargs))
+ #(define* (textpad padding #:optional once?)
+ (ly:export ; this is necessary for using the expression
+ ; directly inside a \notes block
+ (if once?
+ #{ \once \override TextScript #'padding = #$padding #}
+ #{ \override TextScript #'padding = #$padding #})))
+
+ \score {
+ \notes {
+ c'^"1"
+ #(textpad 3.0 #t) % only once
+ c'^"2"
+ c'^"3"
+ #(textpad 5.0)
+ c'^"4"
+ c'^"5"
+
+ }
+ }
+@end lilypond
+
+Here, the variable @code{padding} is a number; music expression
+variables may also be used in a similar fashion, as in the following
+example:
+
+@lilypond[verbatim,raggedright]
+ #(define (with-padding padding)
+ (lambda (music)
+ #{ \override TextScript #'padding = #$padding
+ $music
+ \revert TextScript #'padding #}))
+
+ \score {
+ \notes {
+ c'^"1"
+ \applymusic #(with-padding 3)
+ { c'^"2" c'^"3"}
+ c'^"4"
+ }
+ }
+@end lilypond
+
+The function created by @code{(with-padding 3)} adds @code{\override} and
+@code{\revert} statements around the music given as an argument, and returns
+this new expression. Thus, this example is equivalent to:
+
+@example
+ \score @{
+ \notes @{
+ c'^"1"
+ @{ \override TextScript #'padding = #3
+ @{ c'^"2" c'^"3"@}
+ \revert TextScript #'padding
+ @}
+ c'^"4"
+ @}
+ @}
+@end example
+
+This function may also be defined as a music function:
+
+@lilypond[verbatim,raggedright]
+ withPadding = #(def-music-function (location padding music) (number? ly:music?)
+ #{ \override TextScript #'padding = #$padding
+ $music
+ \revert TextScript #'padding #})
+
+ \score {
+ \notes {
+ c'^"1"
+ \withPadding #3
+ { c'^"2" c'^"3"}
+ c'^"4"
+ }
+ }
+@end lilypond
+
@node Markup programmer interface
@appendixsec Markup programmer interface
@menu
* Markup construction in scheme::
-* Markup command definition::
+* Markup command definition::
@end menu
@node Markup construction in scheme
@menu
-* Context evaluation::
+* Context evaluation::
* Running a function on all layout objects::
@end menu
@node Context evaluation
@appendixsubsec Context evaluation
+@cindex calling code during interpreting
+@cindex @code{\applycontext}
+
Contexts can be modified during interpretation with Scheme code. The
syntax for this is
@example
@node Running a function on all layout objects
@appendixsubsec Running a function on all layout objects
+
+@cindex calling code on layout objects
+@cindex @code{\applyoutput}
+
+
The most versatile way of tuning an object is @code{\applyoutput}. Its
syntax is
@example
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