title: Mix.env/0 equivalent in production env?
body: <p>Mix.env/0 works correctly in <code>mix phoenix.server</code>, but it fails to call in a  production environment which is built with exrm. It makes sense because mix isn't included in the release build, but is there any equivalent of Mix.env/0?</p>
  
  <pre><code>(UndefinedFunctionError) undefined function Mix.env/0 (module Mix is not available)
  </code></pre>
  
  <p>I'm using Mix.env/0 like this in some code:</p>
  
  <pre><code>if Mix.env == :dev do
    # xxxxxx
  else
    # xxxxxx
  end
  </code></pre>