;; declare lambda
($ a (-> (x) (* x 2)))
(assert= 14 (a 7))

;; high order function
($ b (-> (x y) (x (x y))))
(assert= 12 (b a 3))

;; calling function literal
(assert= 7 ( (-> (x y) (+ x y 1)) 2 4 ))

;; syntaxic sugar for function declaration
($ (c n) (* 2 n))
(assert= 18 (c 9))

;; inner variable
($ (d x) ($ y 3) (+ x y))
(assert= 7 (d 4))

;; recursivity
($ (e n)
  (if (eq? 0 n) 1
      (* n (e (- n 1)))))

(assert= 120 (e 5))

;; self keyword
(assert= 720 ((-> (x)
            (if (eq? x 0)
                1
                (* x (self (- x 1))))) 6))

;; inner functions
($ (f n)
  ($ (inner n) (+ n 1))
  (inner (inner n)))

(assert= 3 (f 1))

;; return function
($ (g)
   ($ (inner n) (* 7 n))
   inner)

(assert= 42 ( (g) 6 ))

;; return lambda
($ (h)
   (-> (n)
       (* 3 (- n 2))))

(assert= 15 ( (h) 7 ))

;; closure
($ (i init)
  ($ counter (- init 1))
  (-> ()
    (set! counter (+ counter 1))
    counter))

($ j (i 0))
($ k (i 16))

(assert= 0 (j))
(assert= 16 (k))
(assert= 17 (k))
(assert= 1 (j))
(assert= 2 (j))
(assert= 18 (k))
(assert= 19 (k))
(assert= 3 (j))
(assert= 4 (j))
(assert= 5 (j))
(assert= 20 (k))

($ m 1)
($ (n)
  ($ counter 0)
    (-> ()
      (set! counter (* 2 m))
      (set! m (+ 1 m))
      counter))

($ o (n))
($ p (n))

(assert= 2 (o))
(assert= 4 (o))
(assert= 6 (o))

(assert= 2 (p))
(assert= 4 (p))
(assert= 6 (p))

(assert= 1 m)