title: clojurescript reagent swap! atom negate atom value
body: <p>i tried to invert a value changeval of a reagent atom</p>
  
  <pre><code>(def changeval(reagent/atom 0))
  ...
  ...
  [:input {:type "button" :value "Invert!"
              :on-click #(swap! changeval(not= changeval0 ) ) }]
  </code></pre>
  
  <p>nothing happens, how can I make the changeval = NOT(changeval)</p>