On 3/13/23 1:25 PM, Jean Abou Samra wrote:
Le lundi 13 mars 2023 à 13:04 -0700, Paul Scott a écrit :
I've read your wonderful scheme documentation. I'm still struggling
to make sense of Aaron's simple code
\fixed c' {
c1
\set Score.repeatCommands = #|((volta ,voltaFine)) c4 d c2 \bar
"|." \set Score.repeatCommands = #|((volta #f) (volta ,voltaCont))
f4 g a b
\set Score.repeatCommands = #'((volta #f))
}
I'm extremely familiar with a number of programming languages
including Forth. If one of you could say more about what the line:
\set Score.repeatCommands = #`((volta #f) (volta ,voltaCont))
does and how it relates with
\set Score.repeatCommands = #(list(list 'volta voltaCont))
|I might be able to go farther. |
TIA for any more help with this,
The format of |repeatCommands| is a list where each element is itself
a list. The first element of each sublist (element of the main list)
is a "command", namely a symbol, which can be |volta|, |start-repeat|
or |end-repeat|.
*
If the command is |volta|, LilyPond expects one remaining element
in the sublist, which can be
o a markup, to start a volta bracket and print this text under
it (note that a simple string is also a valid markup),
o |#f| (the boolean /false/), to end a volta bracket previously
started with the first form.
*
If the command is |start-repeat|, it prints a start repeat bar line.
*
If the command is |end-repeat|, it prints an end repeat bar line.
The expression
|#(list (list 'volta voltaCont)) |
uses the |list| function to create a list with one element inside.
That element is |(list 'volta voltaCont)|, which is itself a list with
two elements, |'volta| and |voltaCont|. The first element is a quoted
symbol, so it's not evaluated and remains as a symbol. The second
element is also a symbol but without a quote. Since symbols are not
self-evaluating, but evaluate by looking up variables, this reads the
value of the |voltaCont| variable. So you have
|list | list element 1: | list | list element 1: the symbol volta |
list element 2: the markup contained in the variable voltaCont |
which matches the form for a repeatCommands with one command, "volta",
starting a volta bracket with the text contained in the variable
"voltaCont".
The expression
|#`((volta #f) (volta ,voltaCont)) |
is a quasiquote. Since a quasiquote is “almost a quote”, it means that
Scheme looks literally at what expression you have entered, rather
than evaluating it. Because of the parentheses, it's a list. That list
contains two sublists. The first one is |(volta #f)|. Again, it's
quoted, so it's not evaluated. (If it were evaluated, it would look up
the function “volta” and apply it to the boolean |#f|.) That list is
made of the symbol |volta| and the boolean |#f|.
The second sublist is |(volta ,voltaCont)|. Again, it's quoted, so not
evaluated. The first element is |volta|, a symbol. The second element
has an unquote on it (the comma), so it /does/ get evaluated. It's a
symbol, |voltaCont|, and symbols evaluate by looking up variables, so
it gets the value of |voltaCont| and inserts that markup into the sublist.
The result is
|list | list element 1: | list: | | list element 1: the symbol volta |
| list element 2: the boolean #f | list element 2: | list: | | list
element 1: the symbol volta | | list element 2: the markup contained
in the variable voltaCont |
and it matches the format of |repeatCommands| for two commands: ending
a previously started volta (the first element) and starting a new one
(the second element).
Did it help to read it very verbosely like this?
Probably. I have no excuse for not getting it after this. I won't be
able to spend any more time on for a few hours.
Thank you very much,
Paul
