version that you are working on. See TRANSLATION for details.
@end ignore
+@c \version "2.12.0"
+
@node Scheme tutorial
@appendix Scheme tutorial
Scheme. If you want to know more about Scheme, see
@uref{http://@/www@/.schemers@/.org}.
-The most basic thing of a language is data: numbers, character
+LilyPond uses the GNU Guile implementation of Scheme, which is
+based on the Scheme @qq{R5RS} standard. If you are learning Scheme
+to use with LilyPond, working with a different implementation (or
+referring to a different standard) is not recommended. Information
+on guile can be found at @uref{http://www.gnu.org/software/guile/}.
+The @qq{R5RS} Scheme standard is located at
+@uref{http://www.schemers.org/Documents/Standards/R5RS/}.
+
+The LilyPond installation also 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}
+in the LilyPond installation (for the full path to this directory
+see @ref{Other sources of information}). Alternatively, Windows
+users may simply choose @q{Run} from the Start menu and enter
+@q{guile}.
+
+The most basic concept in a language is data typing: numbers, character
strings, lists, etc. Here is a list of data types that are relevant to
LilyPond input.
In a music file, snippets of Scheme code are introduced with the hash
-mark @code{#}. So, the previous examples translated in LilyPond are
+mark @code{#}. So, the previous examples translated to LilyPond are
@example
##t ##f
a string"
@end example
+Note that LilyPond comments (@code{%} and @code{%@{ %@}}) cannot
+be used within Scheme code. Comments in Guile Scheme are entered
+as follows:
+
+@example
+; this is a single-line comment
+
+#!
+ This a (non-nestable) Guile-style block comment
+ But these are rarely used by Schemers and never in
+ LilyPond source code
+!#
+@end example
+
+Multiple consecutive scheme expressions in a music file can be
+combined using the @code{begin} operator. This permits the number
+of hash marks to be reduced to one.
+
+@example
+#(begin
+ (define foo 0)
+ (define bar 1))
+@end example
+
+If @code{#} is followed by an opening bracket, @code{(}, as in
+the example above, the parser will remain in Scheme mode until
+a matching closing bracket, @code{)}, is found, so further
+@code{#} symbols to introduce a Scheme section are not required.
+
For the rest of this section, we will assume that the data is entered
in a music file, so we add @code{#}s everywhere.
object. @code{thickness} is measured relative to the thickness of
staff lines, so these stem lines will be @code{2.6} times the
width of staff lines. This makes stems almost twice as thick as their
-normal size. To distinguish between variables defined in input files (like
+normal size. To distinguish between variables defined in input files (like
@code{twentyFour} in the example above) and variables of internal
-objects, we will call the latter ``properties'' and the former
-``identifiers.'' So, the stem object has a @code{thickness} property,
-while @code{twentyFour} is an identifier.
+objects, we will call the latter @q{properties} and the former
+@q{variables.} So, the stem object has a @code{thickness} property,
+while @code{twentyFour} is an variable.
-@cindex properties vs. identifiers
-@cindex identifiers vs. properties
+@cindex properties vs. variables
+@cindex variables vs. properties
Two-dimensional offsets (X and Y coordinates) as well as object sizes
(intervals with a left and right point) are entered as @code{pairs}. A
@end example
+@menu
+* Tweaking with Scheme::
+@end menu
+
+@node Tweaking with Scheme
+@appendixsec Tweaking with Scheme
+
+We have seen how LilyPond output can be heavily modified using
+commands like
+@code{\override TextScript #'extra-offset = ( 1 . -1)}. But
+we have even more power if we use Scheme. For a full explanation
+of this, see the @ref{Scheme tutorial}, and
+@ruser{Interfaces for programmers}.
+
+We can use Scheme to simply @code{\override} commands,
+
+TODO Find a simple example
+@c This isn't a valid example with skylining
+@c It works fine without padText -td
+
+@ignore
+@lilypond[quote,verbatim,ragged-right]
+padText = #(define-music-function (parser location padding) (number?)
+#{
+ \once \override TextScript #'padding = #$padding
+#})
+
+\relative c''' {
+ c4^"piu mosso" b a b
+ \padText #1.8
+ c4^"piu mosso" d e f
+ \padText #2.6
+ c4^"piu mosso" fis a g
+}
+@end lilypond
+@end ignore
+
+We can use it to create new commands:
+
+@c Check this is a valid example with skylining
+@c It is - 'padding still works
+
+
+@lilypond[quote,verbatim,ragged-right]
+tempoPadded = #(define-music-function (parser location padding tempotext)
+ (number? string?)
+#{
+ \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"
+ g4 f e d c1
+}
+@end lilypond
+
+
+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
+#})
+
+\relative c''{
+ \pattern c8 c8\f
+ \pattern {d16 dis} { ais16-> b\p }
+}
+@end lilypond
+
+
+
+
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