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;;from clojure.contrib.seq-utils
;;'flatten' written by Rich Hickey,
(defn flatten [x]
(filter (complement sequential?)
(rest (tree-seq sequential? seq x))))
;aprox. translate from paul graham's on lisp to clojure
(defn flatten-ol [x]
(letfn [(rec [x acc]
(cond (not (seq? x)) (cons x acc)
(empty? x) acc
true (recur (first x) (rec (rest x) acc))))]
(lazy-seq (rec x nil))))
;remake with reduce
(defn flatten-ol2 [tree]
(letfn [(rec [acc x]
(if (not (seq? x))
(concat acc [x])
(reduce rec acc x)))]
(lazy-seq (reduce rec () tree))))
; from twitters cgrand and fogus
(defn flatten-cgrand [s] (remove seq? (tree-seq seq? seq s)))
(defn flatten-fogus [x] (if (seq? x)
(lazy-seq (apply concat (map flatten x)))(list x)))
(def bigtree (for [x (range 1 500)] (cons (range 1 5) (range 1 1000))))
;: force the whole tree
;: (btw it would be better to use (take 499 (iterate inc 1)) instead of (range 1 500)
;; because range returns an optimized seq
(dorun (flatten bigtree))
(time (dorun (flatten bigtree)))
(time (dorun (flatten-ol bigtree)))
(time (dorun (flatten-ol2 bigtree)))
(time (dorun (flatten-cgrand bigtree)))
(time (dorun (flatten-fogus bigtree)))
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