Merge branch 'jneeman' of git+ssh://jneem@git.sv.gnu.org/srv/git/lilypond into jneeman

[lilypond.git] / Documentation / user / programming-interface.itely

diff --git a/Documentation/user/programming-interface.itely b/Documentation/user/programming-interface.itely
index 4bc023aab23bb231226d5eb482593dc093aec572..9a62200bbabba423e9f2f34d9c7609a9e1d8af4b 100644 (file)
--- a/Documentation/user/programming-interface.itely
+++ b/Documentation/user/programming-interface.itely
@@ -12,7 +12,7 @@ not familiar with Scheme, you may wish to read our
 * Building complicated functions::  
 * Markup programmer interface::  
 * Contexts for programmers::    
-* Scheme procedures as properties::
+* Scheme procedures as properties::  
 @end menu
 
 
@@ -27,6 +27,7 @@ This section discusses how to create music functions within LilyPond.
 * Paired substitution functions::  
 * Mathematics in functions::    
 * Void functions::              
+* Overview of available music functions::  
 @end menu
 
 @node Overview of music functions
@@ -211,7 +212,6 @@ withAlt = #(define-music-function (parser location mag music) (number? ly:music?
   \withAlt #1.5 {c' c'} c'2 }
 @end lilypond
 
-
 @node Void functions
 @subsection Void functions
 
@@ -237,6 +237,15 @@ noPointAndClick =
 \noPointAndClick   % disable point and click
 @end example
 
+@node Overview of available music functions
+@subsection Overview of available music functions
+
+@c fixme ; this should be move somewhere else?
+The following commands are music functions
+
+@include identifiers.tely
+
+
 
 @node Programmer interfaces
 @section Programmer interfaces
@@ -293,23 +302,35 @@ mixed.  In the following example, a music fragment is stored in the
 variable @code{traLaLa}, and duplicated using Scheme.  The result is
 imported in a @code{\score} block by means of a second variable
 @code{twice}:
-@example
-traLaLa = @{ c'4 d'4 @}
+
+@lilypond[verbatim]
+traLaLa = { c'4 d'4 }
+
+%% dummy action to deal with parser lookahead
+#(display "this needs to be here, sorry!")
 
 #(define newLa (map ly:music-deep-copy
   (list traLaLa traLaLa)))
 #(define twice
   (make-sequential-music newLa))
 
-@{ \twice @}
-@end example
+{ \twice }
+@end lilypond
+
+Due to parser lookahead
 
-In the above example, music expressions can be `exported' from the
+In this example, the assignment happens after parser has verified that
+nothing interesting happens after @code{traLaLa = @{ ... @}}. Without
+the dummy statement in the above example, the @code{newLa} definition
+is executed before @code{traLaLa} is defined, leading to a syntax
+error.
+
+The above example shows how to `export' music expressions from the
 input to the Scheme interpreter.  The opposite is also possible.  By
 wrapping a Scheme value in the function @code{ly:export}, a Scheme
-value is interpreted as if it were entered in LilyPond syntax.  Instead
-of defining @code{\twice}, the example above could also have been
-written as
+value is interpreted as if it were entered in LilyPond syntax.
+Instead of defining @code{\twice}, the example above could also have
+been written as
 @example
 @dots{}
 @{ #(ly:export (make-sequential-music (list newLa))) @}
@@ -594,7 +615,7 @@ have two notes to build the sequence), add @code{SlurEvents} to the
 @code{SequentialMusic} with the two @code{EventChords}.
 
 @example
-doubleSlur = #(def-music-function (parser location note) (ly:music?)
+doubleSlur = #(define-music-function (parser location note) (ly:music?)
          "Return: @{ note ( note ) @}.
          `note' is supposed to be an EventChord."
          (let ((note2 (ly:music-deep-copy note)))
@@ -1153,8 +1174,26 @@ Properties can also be set to a Scheme procedure,
 c b a g b a g b
 @end lilypond
 
-Procedures may also be combined like that with
-"grob closure".  Here is a setting from
+@noindent
+In this case, the procedure is executed as soon as the value of the
+property is requested during the formatting process.
+
+Most of the typesetting engine is driven by such callbacks.
+Properties that typically use callbacks include  
+
+@table @code
+@item stencil
+  The printing routine, that constructs a drawing for the symbol
+@item X-offset
+  The routine that sets the horizontal position
+@item X-extent
+  The routine that computes the width of an object
+@end table
+
+The procedure always takes a single argument, being the grob.
+
+If routines with multiple arguments must be called, the current grob
+can be inserted with a grob closure.  Here is a setting from
 @code{AccidentalSuggestion},
 
 @example
@@ -1167,4 +1206,20 @@ Procedures may also be combined like that with
            (list ly:self-alignment-interface::x-aligned-on-self)))))
 @end example
 
+@noindent
+In this example, both @code{ly:self-alignment-interface::x-aligned-on-self} and
+@code{ly:self-alignment-interface::centered-on-x-parent} are called
+with the grob as argument. The results are added with the @code{+}
+function. To ensure that this addition is properly executed, the whole
+thing is enclosed in @code{ly:make-simple-closure}.
 
+In fact, using a single procedure as property value is equivalent to
+
+@example
+(ly:make-simple-closure (ly:make-simple-closure (list @var{proc})))
+@end example
+
+@noindent
+The inner @code{ly:make-simple-closure} supplies the grob as argument
+to @var{proc}, the outer ensures that result of the function is
+returned, rather than the @code{simple-closure} object.