Re: Cannot pass number variable to \markup.

[Jean Abou Samra]

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

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