It is natural that Clojure does not have loop. Though Clojure does not optimise tail recursion due to limit of JVM, it introduces a similar syntax of Scheme's named let. This syntax doesn't consume stacks too much.
user=> (defn my-zipmap [keys vals]
(loop [my-map {} my-keys (seq keys) my-vals (seq vals)] (if (and my-keys my-vals) (recur (assoc my-map (first my-keys) (first my-vals)) (rest my-keys) (rest my-vals)) my-map)))user=> (my-zipmap [:a :b :c] [1 2 3]){:b 2, :c 3, :a 1}Factorial can be defined as follows.
(defn factorial [n] (loop [cnt n acc 1] (if (zero? cnt) acc (recur (dec cnt) (* acc cnt)))))References:
http://clojure.org/functional_programming
http://clojure.org/special_forms#recur | 当然ながら，言語コアにループはありません．ClojureはJVMを使うため末尾再帰の最適化を行えませんが，Schemeの名前付きletに似た構文を導入しています．この構文を使えばスタックを無駄に消費しません． user=> (defn my-zipmap [keys vals] (loop [my-map {} my-keys (seq keys) my-vals (seq vals)] (if (and my-keys my-vals) (recur (assoc my-map (first my-keys) (first my-vals)) (rest my-keys) (rest my-vals)) my-map)))user=> (my-zipmap [:a :b :c] [1 2 3]){:b 2, :c 3, :a 1}階乗は次のように書けます． (defn factorial [n] (loop [cnt n acc 1] (if (zero? cnt) acc (recur (dec cnt) (* acc cnt)))))参考 http://clojure.org/functional_programming http://clojure.org/special_forms#recur |
Education > Closer to Clojure >