title: Sum of a range of cells that may contain + sign
body: <p>I have a google sheet table with the cells A1, B1 and C1 containing
  either an integer, e.g., <code>12</code> or an expression <code>&lt;integer&gt; + &lt;integer&gt;</code>, e.g.,  <code>12 + 1</code> or <code>12+1</code>.</p>
  
  <p>I want to compute the sum of the cells in <code>D1</code>. Situation</p>
  
  <pre><code>|A1|  B1 | C1|
  --------------
  |1 | 1+1 | 3 |
  </code></pre>
  
  <p>should result in 6. Simply saying <code>D1 = SUM(A1:C1)</code> does not work:
  it ignores the cell <code>B1</code>.</p>
  
  <p>I have found two partial solutions that I cannot combine:</p>
  
  <ul>
  <li><code>SUM(SPLIT(B1;"+"))</code> results in 2</li>
  <li>if I had <code>A2: 1</code>, <code>B2: 4</code> and <code>C2: 9</code>, then <code>ArrayFormula(SUM(SQRT(A2:C2)))</code> results in 6 (sum of square roots of these cells).</li>
  </ul>
  
  <p>(e.g., <code>ArrayFormula(SUM(SUM(SPLIT(A1:C1;"+"))))</code> does not work properly)</p>
  
  <p>How can I solve this problem? Two-step solution i) compute <code>SUM(SPLIT(&lt;cell&gt;;"+"))</code> in a new cell, and ii) compute the sum, is not an option.</p>