title: How align three forms vertically in Elm?
body: <p>1) I don't really get for what purpose <code>Element</code> and <code>Form</code> are different classes. Probably, it causes the following problem.</p>
  
  <p>2)
  My <code>main</code> function maps all signals to a <code>assemble</code> function, which assembles view on each update</p>
  
  <pre><code>assemble: Float -&gt; Float -&gt; Element
  assemble screen_w screen_h =
      [
          background screen_w screen_h,
          header screen_w screen_h,
          info screen_w screen_h
      ] 
          |&gt; collage (round screen_w)  (round screen_h) 
  
  main: Signal Element
  main = 
      assemble
          &lt;~ (toFloat &lt;~ Window.width)
          ~ (toFloat &lt;~ Window.height)
  </code></pre>
  
  <p>This architecture requires <code>header</code> to return <code>Form</code></p>
  
  <p>3)
  <code>header</code> uses one form for text and two other forms to decorate it.</p>
  
  <p>I need to position them one above other and merge into one form.</p>
  
  <pre><code>stripe: Float -&gt; Element
  stripe w = 
      rect w 10
          |&gt; filled black
          |&gt; show
  header: Float -&gt; Float -&gt; Form
  header screen_w screen_h =
      [
          stripe screen_w,
          fromString "My awesome header"
              |&gt; height 64
              |&gt; text
              |&gt; show
          ,
          stripe screen_w
      ]
          |&gt; flow down
          |&gt; toForm
          |&gt; move (0, screen_h/2 - header_size/2 - header_shift)
  </code></pre>
  
  <p>4) The code above displays</p>
  
  <pre><code>&lt;internal structure&gt; 
  &lt;internal structure&gt;
  &lt;internal structure&gt;
  </code></pre>
  
  <p>in place of header and stripes.</p>
  
  <p>It seems that <code>show</code> is unable to inverse <code>toForm</code></p>
  
  <p>because the following</p>
  
  <pre><code>main = 
    show 42
      |&gt; toForm
      |&gt; show
  </code></pre>
  
  <p>also displays</p>
  
  <pre><code>&lt;internal structure&gt; 
  </code></pre>
  
  <p>Can I align three forms one above other, using Elm?</p>