title: subtract from symbols in ruby
body: <p>I would like to find the first valid image among a list in ruby. Here is my code:</p>
  
  <pre><code> if(params[:id])
  
     @image = Image.find_by_id(params[:id])
     while @image.nil?
      :id-- ?
      @image = Image.find_by_id(params[:id])
     end
  </code></pre>
  
  <p>In that block, how can i keep decreasing the id # until a valid image is found? :/</p>
  
  <p>Thanks!</p>