anchor.diff:  ;; => 1
   ----
   
  +
   === Interoperability
   
   There are also `Focus` type that allows you to derive atom like objects from
  
positive.code: === First steps
  
  We'll start by using the most basic lens, the identity lens. We can get the value
  a lens is focused on using the `focus` function in `cats.labs.lens` ns:
  
  [source, clojure]
  ----
  (require '[cats.labs.lens :as l])
  
  (l/focus l/id [0 1 2 3])
  ;; => [0 1 2 3]
  
negative.code: .Run tests on node platform
  [source, text]
  ----
  ./scripts/build
  node ./out/tests.js
  ----
  
  