Logging a variable set by nginx's Lua module

[danslimmon]

I am trying to use the Lua module in nginx to set a variable ("foo") based
on JSON in the body of a request. Then I want to log the value of that
variable to the access log.

Like so: https://gist.github.com/danslimmon/17f5bf4736566737cc65

However, nginx won't start with this configuration. It complains thusly:
https://gist.github.com/danslimmon/f5f789d8af8bbb06b224

Here is my "nginx -V" output:
https://gist.github.com/danslimmon/9ed99c63aa6c04bd1a41/raw/e73bbdfb1c0ead08dd4df80b936dc233542df8bc/gistfile1.txt

Thoughts? Thanks in advance.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,240917,240917#msg-240917