Clojure宏，用于替换字符串模板

问题描述

| 这是我的第一个Clojure宏-我是超级用户。 昨天我发布并完善了字符串模板替换功能。一些人建议可以在编译时替换密钥。这是我的第一次尝试：

(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
      ~@(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

有没有更好的方法来编写此宏？特别是，每个值的扩展版本都没有获得名称空间限定。     

解决方法

我会尽量减少重复的东西。我调整了函数以使用您的累加器宏方法，然后让

replace-templates*

通过

(apply str ...)

完成其余工作。这样，可以在宏中重新使用该函数。

(defn extract-snippets
  [^String text m]
  (loop [text     text
         snippets []]
    (cond
      (zero? (count text))
      snippets

      (.startsWith text \"{\")
      (let [brace (.indexOf text \"}\")]
        (if (neg? brace)
          (conj snippets text)
          (if-let [[_ replacement] (find m (subs text 1 brace))]
            (recur (subs text (inc brace)) (conj snippets replacement))
            (recur (subs text 1)           (conj snippets \\{)))))

        :else
        (let [brace (.indexOf text \"{\")]
          (if (neg? brace)
            (conj snippets text)
            (recur (subs text brace) (conj snippets (subs text 0 brace))))))))

(defn replace-templates*
  [text m]
  (apply str (extract-snippets text m)))

(defmacro replace-templates
  [text m]
  (if (map? m)
    `(apply str ~(extract-snippets text m))
    `(replace-templates* ~text ~m)))

注意：在宏中，您没有取消对ѭ4的引用。因此它只能工作，因为您之前已经对其进行过定义。 with5ѭ不会。     ,将

(defn m {\"foo\" foo*})

更改为

(def m {\"foo\" foo*})

，它似乎可以工作。