anchor.diff:  [source, clojure]
   ----
   (fapply (make-greeter "es") (just "Alex"))
  -;; => #<Just [Hola Alex]>
  +;; => #<Just "Hola Alex">
   
   (fapply (make-greeter "en") (just "Alex"))
  -;; => #<Just [Hello Alex]>
  +;; => #<Just "Hello Alex">
   
   (fapply (make-greeter "it") (just "Alex"))
   ;; => #<Nothing >
  
positive.code: (require '[cats.core :as m])
  
  (m/fmap inc (maybe/just 1))
  ;; => #<Just [2]>
  ----
  
  The *Maybe* type also has another constructor: `nothing`. It represents the absence of a value.
  
negative.code: ----
  (m/bind (maybe/just 1)
          (fn [v] (maybe/just (inc v))))
  ;; => #<Just 2>
  ----
  
  One of the key features of the bind function is that any computation executed within the context of
  