It’s an anonymous function with a single parameter named filtered. It returns a single expression which happens to be jsx.

@fabrao perhaps ...

(defn filter-icon 
  [filtered]
  [Icon {:type "simle-o"
            :style {:color (if filtered "#108ee9"  "#aaa" )}}])

Of course, this is just a sketch. You'll still need to create Icon correctly. And because I know nothing about this Icon (React component?) I'm not sure how to provide it with a "type" etc. But perhaps this helps.