title: rackup undefined local variable or method `env' for Rulers::Application:Class (NameError)
body: <p>I just start reading "Rebuilding Rails" by Noah Gibbs. I'm stuck at page17 where def call(env) is declared.</p>
  
  <p>However, when I run rackup, I came across this error:</p>
  
  <pre><code>undefined local variable or method `env' for Rulers::Application:Class (NameError)
  </code></pre>
  
  <p>How can I define 'env' ?</p>