:javascript
  function login()
  {
    new Ajax.Request($('login_form').action,
    {
      parameters: Form.serialize($('login_form')),
      onCreate: function(){ $('indicator').show(); },
      onComplete: function(){ $('indicator').hide(); },
      onSuccess: function(){ window.location.href = '/'; },
      onFailure: function(){
        new Effect.Shake($('fieldset'));
        $('password').value = '';
        $('password').focus();
      }
    });
  }

= form :action => url(:sessions), :id => 'login_form', :onsubmit => "login(); return false;" do
  %fieldset#fieldset{ :style => "width: 250px;" }
    %legend Papers, comrade?
    %p
      %label{ :for => 'user_name' }
        User Name
        = text_field :name => 'user_name', :id => 'user_name'
    %p
      %label{ :for => 'password' }
        Password
        = password_field :name => 'password', :id => 'password'
    = submit 'Login'
    = indicator