title: Rails slim form_for tag
body: <p>I am having trouble getting a form to work after switching from regular ERB to slim files. Here is the form I am trying to have slim render:</p>
  
  <pre><code>= form_for @student, :url =&gt; students_path(@student), method: :post do |f|
      = f.hidden_field :student_id, :value =&gt; current_user.id
      = f.hidden_field :course_id, :value =&gt; group.id
      = submit_tag "Join this Class!", :class =&gt; "btn btn-primary pull-right join-button"
  </code></pre>
  
  <p>Here was the working code in regular ERB file</p>
  
  <pre><code>&lt;%= form_for @student, :url =&gt; students_path(@student), method: :post do |f| %&gt;
      &lt;%= f.hidden_field :student_id, :value =&gt; current_user.id %&gt;
      &lt;%= f.hidden_field :course_id, :value =&gt; group.id %&gt;
      &lt;%= submit_tag "+ Join", :class =&gt; "btn btn-primary pull-right join-button" %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>This is the error I am currently getting:</p>
  
  <pre><code>undefined local variable or method `f'
  </code></pre>