;;;; This contains some of the core Hy functions used
;;;; to make functional programming slightly easier.
;;;;


(defn _numeric-check [x]
  (if (not (numeric? x))
    (raise (TypeError (.format "{0!r} is not a number" x)))))

(defn cycle [coll]
  "Yield an infinite repetition of the items in coll"
  (setv seen [])
  (for [x coll]
    (yield x)
    (.append seen x))
  (while seen
    (for [x seen]
      (yield x))))

(defn dec [n]
  "Decrement n by 1"
  (_numeric-check n)
  (- n 1))

(defn distinct [coll]
  "Return a generator from the original collection with duplicates
   removed"
  (let [[seen []] [citer (iter coll)]]
    (for [val citer]
      (if (not_in val seen)
        (do
         (yield val)
         (.append seen val))))))

(defn drop [count coll]
  "Drop `count` elements from `coll` and yield back the rest"
  (let [[citer (iter coll)]]
    (try (for [i (range count)]
           (next citer))
         (catch [StopIteration]))
    citer))

(defn even? [n]
  "Return true if n is an even number"
  (_numeric-check n)
  (= (% n 2) 0))

(defn filter [pred coll]
  "Return all elements from `coll` that pass `pred`"
  (let [[citer (iter coll)]]
    (for [val citer]
      (if (pred val)
        (yield val)))))

(defn inc [n]
  "Increment n by 1"
  (_numeric-check n)
  (+ n 1))

(defn instance? [klass x]
  (isinstance x klass))

(defn iterable? [x]
  "Return true if x is iterable"
  (try (do (iter x) true)
       (catch [Exception] false)))

(defn iterate [f x]
  (setv val x)
  (while true
    (yield val)
    (setv val (f val))))

(defn iterator? [x]
  "Return true if x is an iterator"
  (try (= x (iter x))
       (catch [TypeError] false)))

(defn neg? [n]
  "Return true if n is < 0"
  (_numeric-check n)
  (< n 0))

(defn none? [x]
  "Return true if x is None"
  (is x None))

(defn numeric? [x]
  (import numbers)
  (instance? numbers.Number x))

(defn nth [coll index]
  "Return nth item in collection or sequence, counting from 0"
  (if (not (neg? index))
    (if (iterable? coll)
      (try (first (list (take 1 (drop index coll))))
           (catch [IndexError] None))
      (try (get coll index)
           (catch [IndexError] None)))
    None))

(defn odd? [n]
  "Return true if n is an odd number"
  (_numeric-check n)
  (= (% n 2) 1))

(defn pos? [n]
  "Return true if n is > 0"
  (_numeric_check n)
  (> n 0))

(defn remove [pred coll]
  "Return coll with elements removed that pass `pred`"
  (let [[citer (iter coll)]]
    (for [val citer]
      (if (not (pred val))
        (yield val)))))

(defn repeat [x &optional n]
  "Yield x forever or optionally n times"
  (if (none? n)
    (setv dispatch (fn [] (while true (yield x))))
    (setv dispatch (fn [] (for [_ (range n)] (yield x)))))
  (dispatch))

(defn repeatedly [func]
  "Yield result of running func repeatedly"
  (while true
    (yield (func))))

(defn take [count coll]
  "Take `count` elements from `coll`, or the whole set if the total
    number of entries in `coll` is less than `count`."
  (let [[citer (iter coll)]]
    (for [_ (range count)]
      (yield (next citer)))))

(defn take-nth [n coll]
  "Return every nth member of coll
     raises ValueError for (not (pos? n))"
  (if (pos? n)
    (let [[citer (iter coll)] [skip (dec n)]]
      (for [val citer]
        (yield val)
        (for [_ (range skip)]
          (next citer))))
    (raise (ValueError "n must be positive"))))

(defn take-while [pred coll]
  "Take all elements while `pred` is true"
  (let [[citer (iter coll)]]
    (for [val citer]
      (if (pred val)
        (yield val)
        (break)))))

(defn zero? [n]
  "Return true if n is 0"
  (_numeric_check n)
  (= n 0))

(def *exports* ["cycle" "dec" "distinct" "drop" "even?" "filter" "inc"
                "instance?" "iterable?" "iterate" "iterator?" "neg?"
                "none?" "nth" "numeric?" "odd?" "pos?" "remove" "repeat"
                "repeatedly" "take" "take_nth" "take_while" "zero?"])