On 5/7/23 14:23, Jean Abou Samra wrote:
Hi,
I'm adding back the list in CC. Please always keep it so that everyone
can participate.
Le dimanche 07 mai 2023 à 10:45 -0400, dfro a écrit :
Jean,
Thank you, for the fast reply and the clear explanation! Perhaps,
this insight could be put in the Learning Manual, 2.4.1 Organizing
pieces with variables; or, somewhere else on using Scheme in Lilypond.
If I may also ask about the last example in that section of the manual:
<code start>
\version "2.24.1" myWidth = 60 % a number to pass to a \paper
variable % (the unit is millimeter) myName = "Wendy" % a string to
pass to a markup aFivePaper = \paper { #(set-paper-size "a5") }
\paper { \aFivePaper line-width = \myWidth } { c4^\myName }
<code end>
Why can the # symbol be left off of the myWidth variable and other
\paper block variables,
Only \markup mode is special. In normal mode, a number is interpreted
as a number. In markup mode, a number is not interpreted specially so
that \markup { 42 is the answer } works.
and why must the aFivePaper variable be enclosed within '\paper { ... }'?
Unlike TeX macros if you are used to that, LilyPond variables don't
just "insert something in the input" at the point they are used. A
variable is variable in the true programming sense. It is associated
with a value (which has a type). In this case, it does not work to do
aFivePaper = #(set-paper-size "a5")
because that calls set-paper-size immediately, not at the point where
the variable is used, but at the point it is defined. This does
nothing since set-paper-size doesn't have an effect outside of a
\paper block. And since set-paper-size doesn't return a meaningful
value, which in Guile means that it returns a dummy value called
“*unspecified*”, your variable aFivePaper just ends up containing this
dummy value.
With \paper, the variable contains a paper block, and LilyPond will
merge it with the outer paper block if you reference the variable
inside such a block.
Best,
Jean
Jean,
Thank you, for catching my omission of the CC to lilypond-user@gnu.org.
I intended to reply to the group.
The use of variables for the \paper block makes more sense to me.
However, I see that sometimes the numbers have no "#" before them, and
sometimes they do as with:
inst-name-indent = #4.8
...and sometimes they do not, as with:
left-margin-title-page = 45
Also, setting true and false values use "##", as with:
ragged-last-setting = ##f
I am still not comprehending why the "#" is used sometimes and sometimes
not. I am trying to grasp the nuances of how the lilypond language and
the scheme language translate to each other.
Somewhere, in the documentation it talks about lilypond using the "#" to
translate values into scheme language. Leaving off the "#" with numbers
seems to break this rule.
I also have a question about modes. Is normal mode where you input data
outside a music block or without stating a mode explicitly, as with
"\include "..."? I do not see it mentioned in "Notation Reference
Manual, 3.1 Input modes".
Thank you, for the clear explanation of why \paper must be used for a
"set-..." variable outside the main \paper block. That makes sense to me
now.
I hope this is not too far off topic, but your "42 is the answer"
reference led me to find this interesting article that is way over my
head:
https://news.mit.edu/2019/answer-life-universe-and-everything-sum-three-cubes-mathematics-0910.
Thank you, for the help.
Peace,
David
