title: susy argument from sass custom function
body: <p>How can I pass the return value form a custom <strong>Sass</strong> function to a <strong>Susy</strong> function? 
  Or is there any better approach?</p>
  
  <hr>
  
  <p>This works fine:</p>
  
  <pre><code>.foo{ 
      max-width: get_breakpoint('large');
  }
  </code></pre>
  
  <p>But that won't:</p>
  
  <pre><code>.foo{
      @include layout(get_breakpoint('large') 12);
  }
  </code></pre>
  
  <p>Susy just falls back to the default container width instead of using the one from my get_breakpoint() function.</p>
  
  <p>The built uses <strong>Compass</strong>, I have the following function in my <code>config.rb</code>:</p>
  
  <pre><code>module Sass::Script::Functions
      #
      # get breakpoint values from prefs file (json)
      #
      def get_breakpoint(bp)
          if PROJ_PREFS['breakpoint'].include?(bp.value)
              retVal = PROJ_PREFS['breakpoint'][bp.value][0].to_s+'px'
          else
              retVal = bp.to_s
          end
          Sass::Script::String.new(retVal)
      end
  end
  </code></pre>
  
  <p>Software versions: sass (3.4.21), compass (1.0.3), susy (2.2.12).</p>
  
  <p>Many thanks.</p>