The input format supports the notion of variable: in the following
example, a music expression is assigned to a variable with the name
traLaLa
.
traLaLa = \notes { c'4 d'4 }
There is also a form of scoping: in the following example, the
\paper
block also contains a traLaLa
variable, which is
independent of the outer \traLaLa
.
traLaLa = \notes { c'4 d'4 } \paper { traLaLa = 1.0 }
In effect, each input file is a scope, and all \header
,
\midi
and \paper
blocks are scopes nested inside that
toplevel scope.
Both variables and scoping are implemented in the GUILE module system. An anonymous Scheme module is attached to each scope. An assignment of the form
traLaLa = \notes { c'4 d'4 }
is internally converted to a Scheme definition
(define traLaLa Scheme value of “\notes ...
”)
This means that input variables and Scheme variables may be freely
mixed. In the following example, a music fragment is stored in the
variable traLaLa
, and duplicated using Scheme. The result is
imported in a \score
by means of a second variable
twice
:
traLaLa = \notes { c'4 d'4 } #(define newLa (map ly:music-deep-copy (list traLaLa traLaLa))) #(define twice (make-sequential-music newLa)) \score { \twice }
In the above example, music expressions can be `exported' from the
input to the Scheme interpreter. The opposite is also possible. By
wrapping a Scheme value in the function ly:export
, a Scheme
value is interpreted as if it were entered in LilyPond syntax: instead
of defining \twice
, the example above could also have been
written as
... \score { #(ly:export (make-sequential-music newLa)) }
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