Re: Function operating on header

[Timothy Lanfear]

Because that is just a tiny example. I would like to create links to CC
> licenses based on a license field etc.
> What I am lacking here still, is how to do \with-url in Scheme or a
> mechanism to show parts only under a certain condition:
>
> \markup { "Text" ??if \license then \with-url #"url" "License" endif?? }

How about something like this? Comment out  "licence =  ..." to remove 
the copyright statement.

\version "2.20.0"

\header {
  licence = "CC-BY-NC 4.0"
  copyright =
    #(if (defined? 'licence)
      (markup
        #:line
        (#:with-url "https://creativecommons.org/licenses/by-nc/4.0/"; 
licence)))
}

\score {
  c''1
}


--
Timothy Lanfear, Bristol, UK.