Conditionally setting variables in \paper section

[Daniel Thompson]

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Hi Folks

I am trying to modify an shared include file the allow it to switch
the score that uses it between A4 "normal" mode and an cut-down A5
form (for an e-book reader).

I can make set-paper-size conditional using a $(if construct but can't
find a way to conditionally set the margins. I've constructed a tiny
example showing what I have trouble with (it no longer shows my motive
but does show my problem).

- --- cut here ---
\version "2.16.2"
\paper {
$(if (ly:get-option 'binder-margins) #{
  left-margin = 20
  line-width = 180
#})
}
\score \relative { c4 d e f g a b c }
- --- cut here ---

When run "lilypond -dbinder-margins" it issues the following:
- --- cut here ---
test.ly:6:14: error: syntax error, unexpected '=', expecting end of input
  left-margin
              = 20
test.ly:5:0: error: error in #{ ... #}

$(if (ly:get-option 'binder-margins) #{
test.ly:5:0: error: syntax error, unexpected STRING_IDENTIFIER

$(if (ly:get-option 'binder-margins) #{
- --- cut here ---

It works fine without the -dbinder-margins (but then I don't get the
margins set up for a ring binder).

I've tried many "random" things including replacing the lilypond-style
assignment with #(define left-margin 20) but just cannot make it work.

Any ideas?


Thanks.

Daniel.
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