anchor.diff:  handling and recovery.
   
   .Usage example of *try-on* macro.
  -[source, Clojure]
  +[source, clojure]
   ----
   (require '[cats.monad.exception :as exc])
   
  
positive.code: 
  
  .Usage example of `try-or-else` macro.
  [source, Clojure]
  ----
  (exc/try-or-else (+ 1 nil) 2)
  ;; => #<Success [2]>
  ----
  
  .Usage example of `try-or-recover` macro.
  [source, Clojure]
  ----
  (exc/try-or-recover (+ 1 nil)
                      (fn [e]
  
negative.code: in monad state composition.
  
  .Valid function for valid state monad
  [source, clojure]
  ----
  (fn [state]
    "Takes state as argument and return a vector
  