Issue 4296: Let \displayLilyMusic print even repeated durations

[lilypond.git] / Documentation / extending / scheme-tutorial.itely

diff --git a/Documentation/extending/scheme-tutorial.itely b/Documentation/extending/scheme-tutorial.itely
index bad8d261b214cd4e6fc1aff56dafbed1af3b6938..a399570dec32412e13b77457a294999e9af1ee94 100644 (file)
--- a/Documentation/extending/scheme-tutorial.itely
+++ b/Documentation/extending/scheme-tutorial.itely
@@ -275,9 +275,10 @@ Abelson, see
 @node Lists
 @unnumberedsubsubsec Lists
 
-A very common Scheme data structure is the @emph{list}.  Formally, a
-list is defined as either the empty list (represented as @code{'()},
-or a pair whose @code{cdr} is a list.
+A very common Scheme data structure is the @emph{list}.  Formally,
+a @q{proper} list is defined to be either the empty list with its
+input form @code{'()} and length@tie{}0, or a pair whose
+@code{cdr} in turn is a shorter list.
 
 There are many ways of creating lists.  Perhaps the most common is
 with the @code{list} procedure:
@@ -1134,23 +1135,30 @@ will display
 
 By default, LilyPond will print these messages to the console along
 with all the other messages.  To split up these messages and save
-the results of @code{\display@{STUFF@}}, redirect the output to
-a file.
+the results of @code{\display@{STUFF@}}, you can specify an optional
+output port to use:
 
 @example
-lilypond file.ly >display.txt
+@{
+  \displayMusic #(open-output-file "display.txt") @{ c'4\f @}
+@}
 @end example
 
-With a combined bit of Lilypond and Scheme magic, you can actually
-let Lilypond direct just this output to a file of its own:
-
+This will overwrite a previous output file whenever it is called; if you
+need to write more than one expression, you would use a variable for
+your port and reuse it:
 @example
 @{
-  #(with-output-to-file "display.txt"
-      (lambda () #@{ \displayMusic @{ c'4\f @} #@}))
+  port = #(open-output-file "display.txt")
+  \displayMusic \port @{ c'4\f @}
+  \displayMusic \port @{ d'4 @}
+  #(close-output-port port)
 @}
 @end example
 
+Guile's manual describes ports in detail.  Closing the port is actually
+only necessary if you need to read the file before Lilypond finishes; in
+the first example, we did not bother to do so.
 
 A bit of reformatting makes the above information easier to read:
 
@@ -1256,7 +1264,7 @@ The note pitch can be changed by setting this @code{'pitch} property,
        (ly:make-pitch 0 1 0)) ;; set the pitch to d'.
 \displayLilyMusic \someNote
 ===>
-d'
+d'4
 @end example