title: String expression in integer result
body: <p>After a lot of operations I've got some like:</p>
  
  <pre><code>$exr = "2+3/1.5";</code></pre>
  
  <p>How I can get result of this expression? Like this: </p>
  
  <pre><code>$result = (floatval)$exr; // show: 4</code></pre>
  
  <p>Of course it doesn't work. I've got only 2, first symbol.
  Any easy way to solve this?</p>