X-Git-Url: https://git.donarmstrong.com/?a=blobdiff_plain;f=Documentation%2Fextending%2Fscheme-tutorial.itely;h=c75f54630001bc8db7b30ec410e067daf0ac9950;hb=32a34dcef0c0041c6d62677487a380b5c8b85712;hp=7b38a76ef9634833ce2230e349d56444610ffc1d;hpb=f41973ff763d5972a85995b6d40c864281ec6714;p=lilypond.git diff --git a/Documentation/extending/scheme-tutorial.itely b/Documentation/extending/scheme-tutorial.itely index 7b38a76ef9..c75f546300 100644 --- a/Documentation/extending/scheme-tutorial.itely +++ b/Documentation/extending/scheme-tutorial.itely @@ -8,12 +8,11 @@ Guide, node Updating translation committishes.. @end ignore -@c \version "2.14.0" +@c \version "2.16.0" @node Scheme tutorial @chapter Scheme tutorial -@funindex # @cindex Scheme @cindex GUILE @cindex Scheme, in-line code @@ -67,19 +66,31 @@ The LilyPond installation includes the Guile implementation of Scheme. On most systems you can experiment in a Scheme sandbox by opening a terminal window and typing @q{guile}. On some systems, notably Windows, you may need to set the environment variable -@code{GUILE_LOAD_PATH} to the directory @code{../usr/shr/guile/1.8} +@code{GUILE_LOAD_PATH} to the directory @code{../usr/share/guile/1.8} in the LilyPond installation. For the full path to this directory see @rlearning{Other sources of information}. Alternatively, Windows users may simply choose @q{Run} from the Start menu and enter @q{guile}. -Once the guile sandbox is running, you will receive a guile prompt: +However, a hands-on Scheme sandbox with all of Lilypond loaded is +available with this command line: +@example +lilypond scheme-sandbox +@end example + +@noindent +Once the sandbox is running, you will receive a guile prompt: @lisp guile> @end lisp -You can enter Scheme expressions at this prompt to experiment with Scheme. +You can enter Scheme expressions at this prompt to experiment with +Scheme. If you want to be able to use the GNU readline library for +nicer editing of the Scheme command line, check the file +@file{ly/scheme-sandbox.ly} for more information. If you already have +enabled the readline library for your interactive Guile sessions outside +of LilyPond, this should work in the sandbox as well. @node Scheme variables @subsection Scheme variables @@ -148,7 +159,7 @@ and False is @code{#f}. @item Numbers Numbers are entered in the standard fashion, -@code{1} is the (integer) number one, while @code{-1.5} is a +@code{1} is the (integer) number one, while @w{@code{-1.5}} is a floating point number (a non-integer number). @item Strings @@ -600,6 +611,7 @@ guile> (cond ((< a b) "a is less than b") * LilyPond Scheme syntax:: * LilyPond variables:: * Input variables and Scheme:: +* Importing Scheme in LilyPond:: * Object properties:: * LilyPond compound variables:: * Internal music representation:: @@ -607,17 +619,68 @@ guile> (cond ((< a b) "a is less than b") @node LilyPond Scheme syntax @subsection LilyPond Scheme syntax +@funindex $ +@funindex # The Guile interpreter is part of LilyPond, which means that -Scheme can be included in LilyPond input files. The hash mark @code{#} -is used to tell the LilyPond parser that the next value is a Scheme -value. +Scheme can be included in LilyPond input files. There are several +methods for including Scheme in LilyPond. -Once the parser sees a hash mark, input is passed to the Guile -interpreter to evaluate the Scheme expression. The interpreter continues -to process input until the end of a Scheme expression is seen. +The simplest way is to use a hash mark@tie{}@code{#} before a Scheme +expression. -Scheme procedures can be defined in LilyPond input files: +Now LilyPond's input is structured into tokens and expressions, much +like human language is structured into words and sentences. LilyPond +has a lexer that recognizes tokens (literal numbers, strings, Scheme +elements, pitches and so on), and a parser that understands the syntax, +@ruser{LilyPond grammar}. Once it knows that a particular syntax rule +applies, it executes actions associated with it. + +The hash mark@tie{}@code{#} method of embedding Scheme is a natural fit +for this system. Once the lexer sees a hash mark, it calls the Scheme +reader to read one full Scheme expression (this can be an identifier, an +expression enclosed in parentheses, or several other things). After the +Scheme expression is read, it is stored away as the value for an +@code{SCM_TOKEN} in the grammar. Once the parser knows how to make use +of this token, it calls Guile for evaluating the Scheme expression. +Since the parser usually requires a bit of lookahead from the lexer to +make its parsing decisions, this separation of reading and evaluation +between lexer and parser is exactly what is needed to keep the execution +of LilyPond and Scheme expressions in sync. For this reason, you should +use the hash mark@tie{}@code{#} for calling Scheme whenever this is +feasible. + +Another way to call the Scheme interpreter from LilyPond is the use of +dollar@tie{}@code{$} instead of a hash mark for introducing Scheme +expressions. In this case, Lilypond evaluates the code right after the +lexer has read it. It checks the resulting type of the Scheme +expression and then picks a token type (one of several +@code{xxx_IDENTIFIER} in the syntax) for it. It creates a @emph{copy} +of the value and uses that for the value of the token. If the value of +the expression is void (Guile's value of @code{*unspecified*}), nothing +at all is passed to the parser. + +This is, in fact, exactly the same mechanism that Lilypond employs when +you call any variable or music function by name, as @code{\name}, with +the only difference that the name is determined by the Lilypond lexer +without consulting the Scheme reader, and thus only variable names +consistent with the current Lilypond mode are accepted. + +The immediate action of @code{$} can lead to surprises, @ref{Input +variables and Scheme}. Using @code{#} where the parser supports it +is usually preferable. Inside of music expressions, expressions +created using @code{#} @emph{are} interpreted as music. However, +they are @emph{not} copied before use. If they are part of some +structure that might still get used, you may need to use +@code{ly:music-deep-copy} explicitly. + +@funindex $@@ +@funindex #@@ +There are also @q{list splicing} operators @code{$@@} and @code{#@@} +that insert all elements of a list in the surrounding context. + +Now let's take a look at some actual Scheme code. Scheme procedures can +be defined in LilyPond input files: @example #(define (average a b c) (/ (+ a b c) 3)) @@ -625,7 +688,7 @@ Scheme procedures can be defined in LilyPond input files: Note that LilyPond comments (@code{%} and @code{%@{ %@}}) cannot be used within Scheme code, even in a LilyPond input file, because -the Guile interpreter, not the LilyPond parser, is interpreting +the Guile interpreter, not the LilyPond lexer, is reading the Scheme expression. Comments in Guile Scheme are entered as follows: @@ -640,7 +703,7 @@ as follows: @end example For the rest of this section, we will assume that the data is entered -in a music file, so we add @code{#}s at the beginning of each Scheme +in a music file, so we add@tie{}@code{#}s at the beginning of each Scheme expression. All of the top-level Scheme expressions in a LilyPond input file can @@ -682,6 +745,15 @@ twentyFour = #(* 2 twelve) which would result in the number 24 being stored in the LilyPond (and Scheme) variable @code{twentyFour}. +The usual way to refer to Lilypond variables, @ref{LilyPond Scheme +syntax}, is to call them using a backslash, i.e., @code{\twentyFour}. +Since this creates a copy of the value for most of LilyPond's internal +types, in particular music expressions, music functions don't usually +create copies of material they change. For this reason, music +expressions given with @code{#} should usually not contain material that +is not either created from scratch or explicitly copied rather than +directly referenced. + @node Input variables and Scheme @subsection Input variables and Scheme @@ -733,40 +805,74 @@ imported in a @code{\score} block by means of a second variable @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 } +\twice @end lilypond @c Due to parser lookahead -In this example, the assignment happens after the 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. +This is actually a rather interesting example. The assignment will only +take place after the parser has ascertained that nothing akin to +@code{\addlyrics} follows, so it needs to check what comes next. It +reads @code{#} and the following Scheme expression @emph{without} +evaluating it, so it can go ahead with the assignment, and +@emph{afterwards} execute the Scheme code without problem. + +@node Importing Scheme in LilyPond +@subsection Importing Scheme in LilyPond +@funindex $ +@funindex # The above example shows how to @q{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 +placing it after @code{$}, a Scheme value is interpreted as if it were entered in LilyPond syntax. Instead of defining @code{\twice}, the example above could also have been written as @example ... -@{ #(ly:export (make-sequential-music (list newLa))) @} +$(make-sequential-music newLa) +@end example + +You can use @code{$} with a Scheme expression anywhere you could use +@code{\@var{name}} after having assigned the Scheme expression to a +variable @var{name}. This replacement happens in the @q{lexer}, so +Lilypond is not even aware of the difference. + +One drawback, however, is that of timing. If we had been using @code{$} +instead of @code{#} for defining @code{newLa} in the above example, the +following Scheme definition would have failed because @code{traLaLa} +would not yet have been defined. For an explanation of this timing +problem, @ref{LilyPond Scheme syntax}. + +@funindex $@@ +@funindex #@@ +A further convenience can be the @q{list splicing} operators @code{$@@} +and @code{#@@} for inserting the elements of a list in the surrounding +context. Using those, the last part of the example could have been +written as + +@example +... +@{ #@@newLa @} @end example -Scheme code is evaluated as soon as the parser encounters it. To -define some Scheme code in a macro (to be called later), use -@ref{Void functions}, or +Here, every element of the list stored in @code{newLa} is taken in +sequence and inserted into the list, as if we had written + +@example +@{ #(first newLa) #(second newLa) @} +@end example + +Now in all of these forms, the Scheme code is evaluated while the +input is still being consumed, either in the lexer or in the parser. +If you need it to be executed at a later point of time, check out +@ref{Void scheme functions}, or store it in a procedure: @example #(define (nopc) @@ -780,7 +886,7 @@ define some Scheme code in a macro (to be called later), use @knownissues Mixing Scheme and LilyPond variables is not possible with the -@code{--safe} option. +@option{--safe} option. @node Object properties @@ -823,7 +929,7 @@ while @code{twentyFour} is a variable. @subheading Offsets -Two-dimensional offsets (X and Y coordinates) are stored as @code{pairs}. +Two-dimensional offsets (X and Y coordinates) are stored as @emph{pairs}. The @code{car} of the offset is the X coordinate, and the @code{cdr} is the Y coordinate. @@ -838,6 +944,16 @@ this command moves the object 1 staff space to the right, and 2 spaces up. Procedures for working with offsets are found in @file{scm/lily-library.scm}. +@subheading Fractions + +Fractions as used by LilyPond are again stored as @emph{pairs}, this +time of unsigned integers. While Scheme can represent rational numbers +as a native type, musically @samp{2/4} and @samp{1/2} are not the same, +and we need to be able to distinguish between them. Similarly there are +no negative @q{fractions} in LilyPond's mind. So @code{2/4} in LilyPond +means @code{(2 . 4)} in Scheme, and @code{#2/4} in LilyPond means +@code{1/2} in Scheme. + @subheading Extents Pairs are also used to store intervals, which represent a range of numbers @@ -964,18 +1080,16 @@ will display 'SequentialMusic 'elements (list (make-music - 'EventChord - 'elements + 'NoteEvent + 'articulations (list (make-music - 'NoteEvent - 'duration - (ly:make-duration 2 0 1 1) - 'pitch - (ly:make-pitch 0 0 0)) - (make-music 'AbsoluteDynamicEvent 'text - "f"))))) + "f")) + 'duration + (ly:make-duration 2 0 1 1) + 'pitch + (ly:make-pitch 0 0 0)))) @end example By default, LilyPond will print these messages to the console along @@ -987,25 +1101,42 @@ a file. lilypond file.ly >display.txt @end example -With a bit of reformatting, the above information is easier to read, +With a combined bit of Lilypond and Scheme magic, you can actually +let Lilypond direct just this output to a file of its own: + +@example +@{ + #(with-output-to-file "display.txt" + (lambda () #@{ \displayMusic @{ c'4\f @} #@})) +@} +@end example + + +A bit of reformatting makes the above information easier to read: @example (make-music 'SequentialMusic - 'elements (list (make-music 'EventChord - 'elements (list (make-music 'NoteEvent - 'duration (ly:make-duration 2 0 1 1) - 'pitch (ly:make-pitch 0 0 0)) - (make-music 'AbsoluteDynamicEvent - 'text "f"))))) + 'elements (list + (make-music 'NoteEvent + 'articulations (list + (make-music 'AbsoluteDynamicEvent + 'text + "f")) + 'duration (ly:make-duration 2 0 1 1) + 'pitch (ly:make-pitch 0 0 0)))) @end example A @code{@{ ... @}} music sequence has the name @code{SequentialMusic}, and its inner expressions are stored as a list in its @code{'elements} -property. A note is represented as an @code{EventChord} expression, -containing a @code{NoteEvent} object (storing the duration and -pitch properties) and any extra information (in this case, an -@code{AbsoluteDynamicEvent} with a @code{"f"} text property. +property. A note is represented as a @code{NoteEvent} object (storing +the duration and pitch properties) with attached information (in this +case, an @code{AbsoluteDynamicEvent} with a @code{"f"} text property) +stored in its @code{articulations} property. +@funindex{\void} +@code{\displayMusic} returns the music it displays, so it will get +interpreted as well as displayed. To avoid interpretation, write +@code{\void} before @code{\displayMusic}. @node Music properties @subsection Music properties @@ -1014,13 +1145,27 @@ TODO -- make sure we delineate between @emph{music} properties, @emph{context} properties, and @emph{layout} properties. These are potentially confusing. -The @code{NoteEvent} object is the first object of the -@code{'elements} property of @code{someNote}. +Let's look at an example: @example someNote = c' \displayMusic \someNote ===> +(make-music + 'NoteEvent + 'duration + (ly:make-duration 2 0 1 1) + 'pitch + (ly:make-pitch 0 0 0)) +@end example + +The @code{NoteEvent} object is the representation of @code{someNote}. +Straightforward. How about putting c' in a chord? + +@example +someNote = +\displayMusic \someNote +===> (make-music 'EventChord 'elements @@ -1032,6 +1177,9 @@ someNote = c' (ly:make-pitch 0 0 0)))) @end example +Now the @code{NoteEvent} object is the first object of the +@code{'elements} property of @code{someNote}. + The @code{display-scheme-music} function is the function used by @code{\displayMusic} to display the Scheme representation of a music expression. @@ -1076,7 +1224,7 @@ d' @subsection Doubling a note with slurs (example) Suppose we want to create a function that translates input like -@code{a} into @code{a( a)}. We begin by examining the internal +@code{a} into @code{@{ a( a) @}}. We begin by examining the internal representation of the desired result. @example @@ -1086,70 +1234,65 @@ representation of the desired result. 'SequentialMusic 'elements (list (make-music - 'EventChord - 'elements + 'NoteEvent + 'articulations (list (make-music - 'NoteEvent - 'duration - (ly:make-duration 2 0 1 1) - 'pitch - (ly:make-pitch 0 5 0)) - (make-music 'SlurEvent 'span-direction - -1))) + -1)) + 'duration + (ly:make-duration 2 0 1 1) + 'pitch + (ly:make-pitch 0 5 0)) (make-music - 'EventChord - 'elements + 'NoteEvent + 'articulations (list (make-music - 'NoteEvent - 'duration - (ly:make-duration 2 0 1 1) - 'pitch - (ly:make-pitch 0 5 0)) - (make-music 'SlurEvent 'span-direction - 1))))) + 1)) + 'duration + (ly:make-duration 2 0 1 1) + 'pitch + (ly:make-pitch 0 5 0)))) @end example The bad news is that the @code{SlurEvent} expressions -must be added @q{inside} the note (or more precisely, -inside the @code{EventChord} expression). +must be added @q{inside} the note (in its @code{articulations} +property). Now we examine the input, @example +\displayMusic a' +===> (make-music - 'SequentialMusic - 'elements - (list (make-music - 'EventChord - 'elements - (list (make-music - 'NoteEvent - 'duration - (ly:make-duration 2 0 1 1) - 'pitch - (ly:make-pitch 0 5 0)))))) + 'NoteEvent + 'duration + (ly:make-duration 2 0 1 1) + 'pitch + (ly:make-pitch 0 5 0)))) @end example -So in our function, we need to clone this expression (so that we -have two notes to build the sequence), add a @code{SlurEvent} to the -@code{'elements} property of each one, and finally make a -@code{SequentialMusic} with the two @code{EventChords}. +So in our function, we need to clone this expression (so that we have +two notes to build the sequence), add a @code{SlurEvent} to the +@code{'articulations} property of each one, and finally make a +@code{SequentialMusic} with the two @code{EventChords}. For adding to a +property, it is useful to know that an unset property is read out as +@code{'()}, the empty list, so no special checks are required before we +put another element at the front of the @code{articulations} property. @example doubleSlur = #(define-music-function (parser location note) (ly:music?) "Return: @{ note ( note ) @}. - `note' is supposed to be an EventChord." + `note' is supposed to be a single note." (let ((note2 (ly:music-deep-copy note))) - (set! (ly:music-property note 'elements) + (set! (ly:music-property note 'articulations) (cons (make-music 'SlurEvent 'span-direction -1) - (ly:music-property note 'elements))) - (set! (ly:music-property note2 'elements) + (ly:music-property note 'articulations))) + (set! (ly:music-property note2 'articulations) (cons (make-music 'SlurEvent 'span-direction 1) - (ly:music-property note2 'elements))) + (ly:music-property note2 'articulations))) (make-music 'SequentialMusic 'elements (list note note2)))) @end example @@ -1158,9 +1301,12 @@ doubleSlur = #(define-music-function (parser location note) (ly:music?) @subsection Adding articulation to notes (example) The easy way to add articulation to notes is to merge two music -expressions into one context, as explained in -@ruser{Creating contexts}. However, suppose that we want to write -a music function that does this. +expressions into one context, as explained in @ruser{Creating contexts}. +However, suppose that we want to write a music function that does this. +This will have the additional advantage that we can use that music +function to add an articulation (like a fingering instruction) to a +single note inside of a chord which is not possible if we just merge +independent music. A @code{$variable} inside the @code{#@{...#@}} notation is like a regular @code{\variable} in classical LilyPond notation. We @@ -1172,10 +1318,10 @@ know that @noindent will not work in LilyPond. We could avoid this problem by attaching -the articulation to a fake note, +the articulation to an empty chord, @example -@{ << \music s1*0-.-> @} +@{ << \music <> -. -> >> @} @end example @noindent @@ -1187,140 +1333,147 @@ Scheme. We begin by examining our input and desired output, \displayMusic c4 ===> (make-music - 'EventChord - 'elements - (list (make-music - 'NoteEvent - 'duration - (ly:make-duration 2 0 1 1) - 'pitch - (ly:make-pitch -1 0 0)))) + 'NoteEvent + 'duration + (ly:make-duration 2 0 1 1) + 'pitch + (ly:make-pitch -1 0 0)))) ===== % desired output \displayMusic c4-> ===> (make-music - 'EventChord - 'elements + 'NoteEvent + 'articulations (list (make-music - 'NoteEvent - 'duration - (ly:make-duration 2 0 1 1) - 'pitch - (ly:make-pitch -1 0 0)) - (make-music 'ArticulationEvent 'articulation-type - "marcato"))) + "accent")) + 'duration + (ly:make-duration 2 0 1 1) + 'pitch + (ly:make-pitch -1 0 0)) @end example -We see that a note (@code{c4}) is represented as an @code{EventChord} -expression, with a @code{NoteEvent} expression in its elements list. To -add a marcato articulation, an @code{ArticulationEvent} expression must -be added to the elements property of the @code{EventChord} -expression. +We see that a note (@code{c4}) is represented as an @code{NoteEvent} +expression. To add an accent articulation, an @code{ArticulationEvent} +expression must be added to the @code{articulations} property of the +@code{NoteEvent} expression. To build this function, we begin with @example -(define (add-marcato event-chord) - "Add a marcato ArticulationEvent to the elements of `event-chord', - which is supposed to be an EventChord expression." - (let ((result-event-chord (ly:music-deep-copy event-chord))) - (set! (ly:music-property result-event-chord 'elements) - (cons (make-music 'ArticulationEvent - 'articulation-type "marcato") - (ly:music-property result-event-chord 'elements))) - result-event-chord)) +(define (add-accent note-event) + "Add an accent ArticulationEvent to the articulations of `note-event', + which is supposed to be a NoteEvent expression." + (set! (ly:music-property note-event 'articulations) + (cons (make-music 'ArticulationEvent + 'articulation-type "accent") + (ly:music-property note-event 'articulations))) + note-event) @end example The first line is the way to define a function in Scheme: the function -name is @code{add-marcato}, and has one variable called -@code{event-chord}. In Scheme, the type of variable is often clear +name is @code{add-accent}, and has one variable called +@code{note-event}. In Scheme, the type of variable is often clear from its name. (this is good practice in other programming languages, too!) @example -"Add a marcato..." +"Add an accent..." @end example @noindent is a description of what the function does. This is not strictly necessary, but just like clear variable names, it is good practice. -@example -(let ((result-event-chord (ly:music-deep-copy event-chord))) -@end example - -@code{let} is used to declare local variables. Here we use one local -variable, named @code{result-event-chord}, to which we give the value -@code{(ly:music-deep-copy event-chord)}. @code{ly:music-deep-copy} is -a function specific to LilyPond, like all functions prefixed by -@code{ly:}. It is use to make a copy of a music -expression. Here we copy @code{event-chord} (the parameter of the -function). Recall that our purpose is to add a marcato to an -@code{EventChord} expression. It is better to not modify the -@code{EventChord} which was given as an argument, because it may be -used elsewhere. - -Now we have a @code{result-event-chord}, which is a -@code{NoteEventChord} expression and is a copy of -@code{event-chord}. We add the marcato to its @code{'elements} -list property. +You may wonder why we modify the note event directly instead of working +on a copy (@code{ly:music-deep-copy} can be used for that). The reason +is a silent contract: music functions are allowed to modify their +arguments: they are either generated from scratch (like user input) or +are already copied (referencing a music variable with @samp{\name} or +music from immediate Scheme expressions @samp{$(@dots{})} provides a +copy). Since it would be inefficient to create unnecessary copies, the +return value from a music function is @emph{not} copied. So to heed +that contract, you must not use any arguments more than once, and +returning it counts as one use. + +In an earlier example, we constructed music by repeating a given music +argument. In that case, at least one repetition had to be a copy of its +own. If it weren't, strange things may happen. For example, if you use +@code{\relative} or @code{\transpose} on the resulting music containing +the same elements multiple times, those will be subjected to +relativation or transposition multiple times. If you assign them to a +music variable, the curse is broken since referencing @samp{\name} will +again create a copy which does not retain the identity of the repeated +elements. + +Now while the above function is not a music function, it will normally +be used within music functions. So it makes sense to heed the same +contract we use for music functions: the input may be modified for +producing the output, and the caller is responsible for creating copies +if it still needs the unchanged argument itself. If you take a look at +LilyPond's own functions like @code{music-map}, you'll find that they +stick with the same principles. + +Where were we? Now we have a @code{note-event} we may modify, not +because of using @code{ly:music-deep-copy} but because of a long-winded +explanation. We add the accent to its @code{'articulations} list +property. @example (set! place new-value) @end example -Here, what we want to set (the @q{place}) is the @code{'elements} -property of @code{result-event-chord} expression. +Here, what we want to set (the @q{place}) is the @code{'articulations} +property of @code{note-event} expression. @example -(ly:music-property result-event-chord 'elements) +(ly:music-property note-event 'articulations) @end example @code{ly:music-property} is the function used to access music properties -(the @code{'elements}, @code{'duration}, @code{'pitch}, etc, that we +(the @code{'articulations}, @code{'duration}, @code{'pitch}, etc, that we see in the @code{\displayMusic} output above). The new value is the -former @code{'elements} property, with an extra item: the +former @code{'articulations} property, with an extra item: the @code{ArticulationEvent} expression, which we copy from the @code{\displayMusic} output, @example (cons (make-music 'ArticulationEvent - 'articulation-type "marcato") - (ly:music-property result-event-chord 'elements)) + 'articulation-type "accent") + (ly:music-property result-event-chord 'articulations)) @end example -@code{cons} is used to add an element to a list without modifying -the original list. This is what we want: the same list as before, -plus the new @code{ArticulationEvent} expression. The order -inside the @code{'elements} property is not important here. +@code{cons} is used to add an element to the front of a list without +modifying the original list. This is what we want: the same list as +before, plus the new @code{ArticulationEvent} expression. The order +inside the @code{'articulations} property is not important here. -Finally, once we have added the marcato articulation to its @code{elements} -property, we can return @code{result-event-chord}, hence the last line of -the function. +Finally, once we have added the accent articulation to its +@code{articulations} property, we can return @code{note-event}, hence +the last line of the function. -Now we transform the @code{add-marcato} function into a music -function, +Now we transform the @code{add-accent} function into a music +function (a matter of some syntactic sugar and a declaration of the type +of its sole @q{real} argument). @example -addMarcato = #(define-music-function (parser location event-chord) +addAccent = #(define-music-function (parser location note-event) (ly:music?) - "Add a marcato ArticulationEvent to the elements of `event-chord', - which is supposed to be an EventChord expression." - (let ((result-event-chord (ly:music-deep-copy event-chord))) - (set! (ly:music-property result-event-chord 'elements) - (cons (make-music 'ArticulationEvent - 'articulation-type "marcato") - (ly:music-property result-event-chord 'elements))) - result-event-chord)) + "Add an accent ArticulationEvent to the articulations of `note-event', + which is supposed to be a NoteEvent expression." + (set! (ly:music-property note-event 'articulations) + (cons (make-music 'ArticulationEvent + 'articulation-type "accent") + (ly:music-property note-event 'articulations))) + note-event) @end example We may verify that this music function works correctly, @example -\displayMusic \addMarcato c4 +\displayMusic \addAccent c4 @end example @@ -1353,7 +1506,7 @@ TODO Find a simple example @lilypond[quote,verbatim,ragged-right] padText = #(define-music-function (parser location padding) (number?) #{ - \once \override TextScript #'padding = #$padding + \once \override TextScript #'padding = #padding #}) \relative c''' { @@ -1375,16 +1528,16 @@ We can use it to create new commands: @lilypond[quote,verbatim,ragged-right] tempoPadded = #(define-music-function (parser location padding tempotext) - (number? string?) + (number? markup?) #{ - \once \override Score.MetronomeMark #'padding = $padding - \tempo \markup { \bold $tempotext } + \once \override Score.MetronomeMark #'padding = #padding + \tempo \markup { \bold #tempotext } #}) \relative c'' { \tempo \markup { "Low tempo" } c4 d e f g1 - \tempoPadded #4.0 #"High tempo" + \tempoPadded #4.0 "High tempo" g4 f e d c1 } @end lilypond @@ -1395,7 +1548,7 @@ Even music expressions can be passed in: @lilypond[quote,verbatim,ragged-right] pattern = #(define-music-function (parser location x y) (ly:music? ly:music?) #{ - $x e8 a b $y b a e + #x e8 a b #y b a e #}) \relative c''{