這是我的第一個Clojure宏 - 我是一個超級菜鳥。用於字符串模板替換的Clojure宏
昨天我posted並精煉了一個字符串模板替換函數。有幾個人建議在編譯時可以更換密鑰。這是我第一次嘗試:
(defn replace-templates*
"Return a String with each occurrence of a substring of the form {key}
replaced with the corresponding value from a map parameter.
@param str the String in which to do the replacements
@param m a map of template->value
@thanks kotarak https://stackoverflow.com/questions/6112534/
follow-up-to-simple-string-template-replacement-in-scala-and-clojure"
[^String text m]
(let [builder (StringBuilder.)]
(loop [text text]
(cond
(zero? (count text))
(.toString builder)
(.startsWith text "{")
(let [brace (.indexOf text "}")]
(if (neg? brace)
(.toString (.append builder text))
(if-let [[_ replacement] (find m (subs text 1 brace))]
(do
(.append builder replacement)
(recur (subs text (inc brace))))
(do
(.append builder "{")
(recur (subs text 1))))))
:else
(let [brace (.indexOf text "{")]
(if (neg? brace)
(.toString (.append builder text))
(do
(.append builder (subs text 0 brace))
(recur (subs text brace)))))))))
(def foo* 42)
(def m {"foo" foo*})
(defmacro replace-templates
[text m]
(if (map? m)
`(str
[email protected](loop [text text acc []]
(cond
(zero? (count text))
acc
(.startsWith text "{")
(let [brace (.indexOf text "}")]
(if (neg? brace)
(conj acc text)
(if-let [[_ replacement] (find m (subs text 1 brace))]
(recur (subs text (inc brace)) (conj acc replacement))
(recur (subs text 1) (conj acc "{")))))
:else
(let [brace (.indexOf text "{")]
(if (neg? brace)
(conj acc text)
(recur (subs text brace) (conj acc (subs text 0 brace))))))))
`(replace-templates* ~text m)))
(macroexpand '(replace-templates "this is a {foo} test" {"foo" foo*}))
;=> (clojure.core/str "this is a " foo* " test")
(println (replace-templates "this is a {foo} test" {"foo" foo*}))
;=> this is a 42 test
(macroexpand '(replace-templates "this is a {foo} test" m))
;=> (user/replace-templates* "this is a {foo} test" user/m)
(println (replace-templates "this is a {foo} test" m))
;=> this is a 42 test
有沒有更好的方法來編寫這個宏?特別是每個值的擴展版本都沒有獲得命名空間限定。
用'(地圖?m)'好主意。 :) – kotarak 2011-05-26 20:35:53