title: F#, assignment operator vs set operator
body: <p>I have started with F# and some code structure wonder me. For example:</p>
  
  <p>I have next code:</p>
  
  <pre><code>let mutable s = 10
  s &lt;- 1 + s
  printf "%i" s
  </code></pre>
  
  <p>Everything is clear from math side. I marked "s" as mutable and assigned the new value to "s". Result is 11.</p>
  
  <p>Let me try other part of code:</p>
  
  <pre><code>let mutable s = 10
  s = 1 + s
  printf "%i" s
  </code></pre>
  
  <p>This code was worked. But I see that <code>s = 1 + s</code> is a bit strange from the math side. Result of executing of this was 10. </p>
  
  <p>My question, what go on in the last sample? Why didn't I get a error? Is <code>s = 1 + s</code> just ignored? Why? I didn't get any error in the output.</p>