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;;;; cf. http://riktor.hatenablog.com/entry/2012/07/22/223937 | |
(def counter | |
(let [cnt (atom 0)] | |
(fn [] (swap! cnt inc)))) | |
(counter) | |
(counter) | |
(counter) | |
(defn make-counter [] | |
(let [cnt (atom 0)] | |
(fn [] (swap! cnt inc)))) | |
(def counter1 (make-counter)) | |
(def counter2 (make-counter)) | |
(counter1) | |
(counter1) | |
(counter1) | |
(counter2) | |
(counter2) | |
(counter1) | |
(def counter | |
(let [cnt (atom 0)] | |
(fn [msg & [arg]] | |
(let [delta (or arg 1)] | |
(case msg | |
:inc (swap! cnt + delta) | |
:dec (swap! cnt - delta)))))) | |
(counter :inc) | |
(counter :inc 2) | |
(counter :dec) | |
(counter :dec 2) | |
(sort (let [cnt (atom 0)] | |
(fn [a b] | |
(println (swap! cnt inc)) | |
(< a b))) | |
'(1 33 4 -2 3 1 432)) | |
(defmacro defn-memoized [fn-name args & body] | |
`(let [memo# (atom {})] | |
(defn ~fn-name [~@args] | |
(if-let [n# (get @memo# [~@args])] | |
n# | |
(let [m# (do ~@body)] | |
(swap! memo# assoc [~@args] m#) | |
m#))))) | |
(defn-memoized fib-memoized [n] | |
(if (or (= n 0) (= n 1)) | |
1 | |
(+ (fib-memoized (- n 1)) | |
(fib-memoized (- n 2))))) |
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