Carp/examples/sumtypes.carp

(use Maybe)
(Project.no-echo)
(Project.config "print-ast" true)

;; Generic types
(defn generic-sumtypes [s]
  (match s
    (Maybe.Nothing) @"Nada"
    (Maybe.Just x)  (str* "Something like " (str x))
    ))

;; A more convenient syntax when doing C-style enums
(deftype Grade A B C)

(use Grade)

(defn grade-value [g]
  (match (the Grade g)
    A 20
    B 15
    C 10))

;; Figure out which type to use when some cases have the same name
(deftype Commands
  StandGround
  Fire
  Retreat)

(deftype Elements
  Water
  Fire ;; <- name clash!
  Earth
  Air)

(use Commands)
(use Elements)

(defn figure-out-sumtype [x]
  (match x
    Fire (Water)
    Air (Earth)))

;; Variable shadowing inside match
(defn confusion [x]
  (match x
    (Maybe.Just x) x
    (Maybe.Nothing) @"Nope"))

;; Wildcards
(defn wildcard [x]
  (match x
    Nothing @"No"
    _ @"Yes"
    ))

(deftype Name
  (Simple [String String])
  (Fancy [String String String]))

(use Name)

(defn wildcards-inside [name]
  (match name
    (Simple _ _) 1
    (Fancy _ _ _) 2))

;; Recursive sumtype
;; (deftype JSON
;;   (Str [String])
;;   (Num [Double])
;;   (Arr [(Array JSON)])
;;   (Obj [(Map String JSON)]))

(defn main []
  (do
    (println* (generic-sumtypes (Maybe.Just 123)))
    (println* (generic-sumtypes (the (Maybe Int) (Maybe.Nothing))))
    (println* &(figure-out-sumtype (Elements.Fire)))
    (println* "Grade.B has value " (grade-value (Grade.B)))
    (println* (confusion (Just @"Yo")))
    (println* (wildcard (Just @"Woop")))
    (println* (wildcards-inside (Simple @"Erik" @"Svedäng")))))