anchor.diff:  (require '[cats.monad.maybe :as maybe])
   
   (maybe/just 2)
  -;; => #<Just [2]>
  +;; => #<Just 2>
   ----
   
   The `just` function is a constructor of Just type that is part of Maybe monad.
  
positive.code: [source, clojure]
  ----
  (maybe/just 1)
  ;; => #<Just [1]>
  
  (maybe/nothing)
  ;; => #<Nothing >
  
negative.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.
  