lilypond-book fails when using Latex macros in options

[John Szwast]

I want to specify a lilypond environment option with a Latex macro, but 
lilypond-book fails when I try.

\documentclass{article}
\newcommand\staffsize{14}
\begin{document}
%       \begin[staffsize=14]{lilypond}  % This works
        \begin[staffsize=\staffsize]{lilypond}  % This doesn't
        \end{lilypond}
\end{document}

The output from lilypond-book is

$ lilypond-book doc.lytex --pdf
lilypond-book (GNU LilyPond) 2.16.2
Reading doc.lytex...
Running `pdflatex' on file `/tmp/tmpJwcX6r.tex' to detect default page 
settings.

Dissecting...
Writing snippets...
Processing...
Running lilypond...
GNU LilyPond 2.16.2
Processing `snippet-map--2549988710888344390.ly'
Parsing...
Processing `doc.lytex'
Parsing...
doc.lytex:10:1: error: GUILE signaled an error for the expression beginning 
here
#
 (set-global-staff-size \staffsize)
Unbound variable: \staffsize
Layout output to `c8/lily-484264f5.eps'...
Converting to `c8/lily-484264f5.pdf'...
Writing c8/lily-484264f5-systems.texi...
Writing c8/lily-484264f5-systems.tex...
Writing c8/lily-484264f5-systems.count...
fatal error: failed files: "c8/lily-484264f5.ly"
command failed: /usr/bin/lilypond --formats=ps -dbackend=eps  -I  "." --
formats=eps --pdf -dinclude-eps-fonts -dgs-load-fonts  -deps-box-
padding=3.000000  -dread-file-list -dno-strip-output-dir  
"/home/daddy/Projects/lilypond_book_mwe/snippet-names-
-2549988710888344390.ly"
Child returned 1