标签：clojure

常用宏

infix宏解析人的四则运算书写格式并执行

(defmacro infix
  "Use this macro when you pine for the notation of your childhood"
  [infixed]
  (list (second infixed) (first infixed) (last infixed)))

(infix (1 + 1))
; => 2

user=> (macroexpand ‘(ignore-last-operand (+ 1 2 10)))
(+ 1 2)

-> 宏改变从右到左的阅读方式

(defn read-resource
  "Read a resource into a string"
  [path]
  (read-string (slurp (clojure.java.io/resource path))))

(defn read-resource
  [path]
  (-> path
      clojure.java.io/resource
      slurp
      read-string))

binding宏

binding宏用来创建线程专属的变量，在多线程中很常用。

user=> (def ^:dynamic x 1)
user=> (def ^:dynamic y 1)
user=> (+ x y)
2
 
user=> (binding [x 2 y 3]
         (+ x y))
5
 
user=> (+ x y)
2

when宏

可以接受一堆参数，如果条件为真，这些参数都依次被求值，返回最后一个求值的结果。when的实现是用(if 和 (do。

(macroexpand ‘(when boolean-expression
                expression-1
                expression-2
                expression-3))
; =>
(if boolean-expression
  (do expression-1
      expression-2
      expression-3))

Clojure语言十四 常用宏

标签：clojure

原文地址：http://blog.csdn.net/csfreebird/article/details/49444467