anchor.diff:  ;; => #<Just "Hello Alex">
   
   (fapply (make-greeter "it") (just "Alex"))
  -;; => #<Nothing >
  +;; => #<Nothing>
   ----
   
   Moreover, the applicative functor comes with the *pure* function, which allows
  
positive.code: ;; => #<Just 6>
  
  (add-m (just 1) (nothing) (just 3))
  ; => #<Nothing >
  
  (add-m (just 1) nil (just 3))
  ;; => nil
  
negative.code: [source, clojure]
  ----
  (m/fmap inc (nothing))
  ;; => #<Nothing>
  ----
  
  Oh, awesome, instead of raising a `NullPointerException`, it just returns *nothing*. Another
  