Clojure's Solutions to the Expression Problem(infoq.com)

  *But beware. Once you see, you cannot un-see the fact that…*

  Any sufficiently complicated data system contains an ad-hoc, informally-specified, bug-ridden, slow implementation of half of a bitemporal database.

  — Henderson's Tenth Law. (= henderson https://github.com/jarohen) 

  (defprotocol IPageObject
    "Each PageObject MUST implement the IPageObject protocol."
    (page-object [this])
    (exists? [this])
    (visible? [this]))

  (defrecord Checkbox [target-css]
    IPageObject
    (page-object [this]
      this)
    (exists? [this]
      ;; webdriver check if target-css exists
      )
    (visible? [this]
      ;; webdriver check if target-css is visible
      )

    Selectable
    (select [this]
      ;; webdriver select the target
      )

    (deselect [this]
      ;; webdriver undo selection
      )
  
    (selected? [this]
      ;; webdriver return true if target selected
      )  

    Value
    (get-value [this]
      ;; webdriver return current selection state
      (selected? this)))