janet/examples/iterators.dst

###
###
### Iterators
###
###

(def iter (do
            (defn array-iter [x]
              (def len (length x))
              (var i 0)
              {:more (fn [] (< i len))
               :next (fn []
                       (def ret (get x i))
                       (:= i (+ i 1))
                       ret)})
            (def iters {
                        :array array-iter
                        :tuple array-iter
                        :struct identity})
            (fn [x]
              (def makei (get iters (type x)))
              (if makei (makei x) (error "expected sequence")))))

(defn range2 [bottom top]
  (var i bottom)
  {
   :more (fn [] (< i top))
   :next (fn []
           (def ret i)
           (:= i (+ i 1))
           ret)
   })

(defn range [top] (range2 0 top))

(defn doiter [itr]
  (def {:more more :next next} (iter itr))
  (while (more) (next)))

(defn foreach [itr f]
  (def {:more more :next next} (iter itr))
  (while (more) (f (next))))

(defn iter2array [itr]
  (def {:more more :next next} (iter itr))
  (def a @[])
  (while (more) (array.push a (next)))
  a)

(defn map [f itr]
  (def {:more more :next next} (iter itr))
  {:more more :next (fn [] (f (next)))})

(defn reduce [f start itr]
  (def itr (iter itr))
  (def {:more more :next next} itr)
  (if (more)
    (reduce f (f start (next)) itr)
    start))

(defn filter [pred itr]
  (def itr (iter itr))
  (def {:more more :next next} itr)
  (var alive true)
  (var temp nil)
  (var isnew true)
  (defn nextgood []
    (if alive
      (if (more)
        (do
          (def n (next))
          (if (pred n) n (nextgood)))
        (:= alive false))))
  (defn nnext [] (def ret temp) (:= temp (nextgood)) ret)
  (defn nmore [] (when isnew (:= isnew false) (nnext)) alive)
  {:more nmore :next nnext})

(defn pairs [x]
  (var lastkey (next x nil))
  {
   :more (fn [] lastkey)
   :next (fn []
           (def ret (tuple lastkey (get x lastkey)))
           (:= lastkey (next x lastkey))
           ret)
   })

(defn keys [x]
  (var lastkey (next x nil))
  {
   :more (fn [] lastkey)
   :next (fn []
           (def ret lastkey)
           (:= lastkey (next x lastkey))
           ret)
   })

(defn values [x]
  (var lastkey (next x nil))
  {
   :more (fn [] lastkey)
   :next (fn []
           (def ret (get x lastkey))
           (:= lastkey (next x lastkey))
           ret)
   })