anchor.diff:  
   Let's convert this factory to use Maybe type:
   
  -[source, Clojure]
  +[source, clojure]
   ----
   (defn make-greeter
     [^String lang]
  
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: what that container is, you can use `return` or `pure` functions:
  
  .Usage of return function in bind context.
  [source,clojure]
  ----
  (bind (just 1)
        (fn [v]
  