anchor.diff:  handling and recovery.
   
   .Usage example of *try-on* macro.
  -[source, Clojure]
  +[source, clojure]
   ----
   (require '[cats.monad.exception :as exc])
   
  
positive.code: 
  Let's see one example using *fmap* over *just* instance:
  
  .Example using fmap over *just*.
  [source, Clojure]
  ----
  (require '[cats.core :as m]
           '[cats.monad.maybe :refer [just]])
  
negative.code: Let's look at one example before explaining the details:
  
  .Lazy composition of computations
  [source, clojure]
  ----
  (m/mlet [state (m/get-state)
           _     (m/put-state (next state))]
  