location ~{location} {
  ~(when root (format "root %s;" root))
  index  ~(apply str (interpose " " index));
  ~(when proxy_pass (format "proxy_pass %s;" proxy_pass))
  ~(when passenger-enabled (format "passenger_enabled %s;" passenger-enabled))
  ~(when rails-env (format "rails_env %s;" rails-env))
}
