@node Scheme tutorial
@appendix Scheme tutorial
-@cindex @code{#}
+@findex #
@cindex Scheme
@cindex GUILE
@cindex Scheme, in-line code
@cindex LISP
LilyPond uses the Scheme programming language, both as part of the
-input syntax, and as internal mechanism to glue together modules of
-the program. This section is a very brief overview of entering data in
-Scheme.@footnote{If you want to know more about Scheme, see
-@uref{http://@/www@/.schemers@/.org}.}
+input syntax, and as internal mechanism to glue modules of the program
+together. This section is a very brief overview of entering data in
+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
strings, lists, etc. Here is a list of data types that are relevant to
@item Booleans
Boolean values are True or False. The Scheme for True is @code{#t}
and False is @code{#f}.
-@cindex @code{##t}
-@cindex @code{##f}
+@findex ##t
+@findex ##f
@item Numbers
Numbers are entered in the standard fashion,
@code{1} is the (integer) number one, while @code{-1.5} is a
-floating point number (a non-integer number).
+floating point number (a non-integer number).
@item Strings
Strings are enclosed in double quotes,
mark @code{#}. So, the previous examples translated in LilyPond are
@example
-##t ##f
+##t ##f
#1 #-1.5
#"this is a string"
#"this
@lisp
#(+ 1 2)
- @result{} #3
+ @result{} #3
@end lisp
The arrow @result{} shows that the result of evaluating @code{(+ 1 2)}
@lisp
#(+ 1 (* 3 4))
- @result{} #(+ 1 12)
+ @result{} #(+ 1 12)
@result{} #13
@end lisp
These calculations are examples of evaluations; an expression like
@code{(* 3 4)} is replaced by its value @code{12}. A similar thing
-happens with variables. After defining a variable
+happens with variables. After defining a variable
@example
-twelve = #12
+twelve = #12
@end example
@noindent
variables can also be used in expressions, here
@example
-twentyFour = #(* 2 twelve)
-@end example
+twentyFour = #(* 2 twelve)
+@end example
@noindent
the number 24 is stored in the variable @code{twentyFour}.
The same assignment can be done in completely in Scheme as well,
@example
-#(define twentyFour (* twelve))
+#(define twentyFour (* 2 twelve)
@end example
The @emph{name} of a variable is also an expression, similar to a
#'twentyFour
@end example
-@cindex @code{#'symbol}
+@findex #'symbol
@cindex quoting in Scheme
-The quote mark @code{'} prevents Scheme interpreter from substituting
+The quote mark @code{'} prevents the Scheme interpreter from substituting
@code{24} for the @code{twentyFour}. Instead, we get the name
@code{twentyFour}.
@end example
This instruction adjusts the appearance of stems. The value @code{2.6}
-is put into a the @code{thickness} variable of a @code{Stem}
-object. This makes stems almost twice as thick as their normal size.
-To distinguish between variables defined in input files (like
+is put into the @code{thickness} variable of a @code{Stem}
+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
@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.
@cindex properties vs. identifiers
-@cindex identifiers vs. properties
+@cindex identifiers 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
is entered as @code{(first . second)} and, like symbols, they must be quoted,
@example
-\override TextScript #'extra-offset = #'(1 . 2)
-@end example
+\override TextScript #'extra-offset = #'(1 . 2)
+@end example
This assigns the pair (1, 2) to the @code{extra-offset} property of the
-TextScript object. This moves the object 1 staff space to the right,
-and 2 spaces up.
+TextScript object. These numbers are measured in staff-spaces, so
+this command moves the object 1 staff space to the right, and 2 spaces up.
The two elements of a pair may be arbitrary values, for example
#'(1 2 "string" #f)
@end example
-We have been using lists all along. A calculation, like @code{(+ 1
-2)} is also a list (containing the symbol @code{+} and the numbers 1
+We have been using lists all along. A calculation, like @code{(+ 1 2)}
+is also a list (containing the symbol @code{+} and the numbers 1
and@tie{}2). Normally lists are interpreted as calculations, and the
Scheme interpreter substitutes the outcome of the calculation. To enter a
-list, we stop evaluation. This is done by quoting the list with a
+list, we stop the evaluation. This is done by quoting the list with a
quote @code{'} symbol. So, for calculations do not use a quote.
Inside a quoted list or pair, there is no need to quote anymore. The
projects / lilypond.git / blobdiff