anchor.diff:  (defn make-greeter
     [^String lang]
     (condp = lang
  -    "es" (just (fn [name] (str "Hola " name)))
  -    "en" (just (fn [name] (str "Hello " name)))
  -    (nothing)))
  +    "es" (maybe/just (fn [name] (str "Hola " name)))
  +    "en" (maybe/just (fn [name] (str "Hello " name)))
  +    (maybe/nothing)))
   ----
   
   As you can see, this version of the factory differs only slightly from the
  
positive.code: .Example using fmap over *nothing*.
  [source, clojure]
  ----
  (m/fmap inc (nothing))
  ;; => #<Nothing>
  ----
  
  
negative.code: 
  [source, clojure]
  ----
  (m/foldl (fn [acc v] (+ acc v)) 0 [1 2 3 4 5])
  ;; => 15
  ----
  
  