String 用于字符串模板替换的Clojure宏
这是我的第一个Clojure宏——我是uber noob 昨天我改进了一个字符串模板替换函数。一些人建议可以在编译时替换密钥。这是我的第一次尝试:String 用于字符串模板替换的Clojure宏,string,macros,clojure,String,Macros,Clojure,这是我的第一个Clojure宏——我是uber noob 昨天我改进了一个字符串模板替换函数。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 t
(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这个宏?特别是,每个值的扩展版本没有获得名称空间限定。将
(defn m{“foo”foo*})
更改为(def m{“foo”foo*})
,它似乎可以工作。我会尝试减少重复的内容。我调整了函数以使用累加器的宏方法,并让替换模板*
通过(应用str…
)执行其余操作。这样就可以在宏中重复使用该函数
(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,您没有解压缩
m
。所以它只起作用,因为你以前定义过它。使用(让[m{“a”“b”}(替换模板“…”m))
使用(map?m)
:)这个主意不错谢谢你的重构。我正在读《让Lambda过去》(Doug Hoyte)——这本书都是关于常见的Lisp宏的。还感谢您在~m
上给出的答案。我之前试过,但由于宏中的其他问题,没有注意到这是“正确”的答案。