title: This value is not a function and cannot be applied
body: <p>Pretty simple function for operation of negation.</p>
  
  <pre><code>let negation (value:option&lt;bool&gt;) =
     match value with
     |Some true -&gt; Some false
     |Some false -&gt; Some true
     |None -&gt; failwith "OOPS"
  </code></pre>
  
  <p>but when i call it:</p>
  
  <pre><code>negation Some true 
  </code></pre>
  
  <p>it complains that </p>
  
  <pre><code>This value is not a function and cannot be applied
  </code></pre>