Question

我正在尝试使用此技术将值绑定到宏中传入的符号。

(defmacro t2macro [all-bindings body] (reduce (fn [acc [v binding]]
                                                 `(let [~v ~binding] ~acc))
                                                   `(do ~@body) all-bindings))
#'plans-client.mock/t2macro
plans-client.mock> (t2macro [[a 1] [b 2]] (print (+ a b)))
3

此简化版本可以正常工作。现在，当我尝试在宏列表的上下文中使用相同的技术时，

(defmacro with-mocked-grpc
  [mocked-responses & body]
  (let [mocks (for [[mock-name [status response]] (partition-all 2 mocked-responses)]
                (let [conformed-resp
                      (specs-util/conform-or-throw ::response response)
                      generated-resp (check-response conformed-resp mock-name)
                      bindings       (check-bindings generated-resp)]
                  (with-meta [mock-name [status generated-resp]]
                    (when bindings {:bindings bindings}))))
        all-bindings (map (fn [m] (:bindings (meta m))) mocks)]
    (reduce (fn [acc [v binding]]
              `(let [~v ~binding] ~acc))
            `(do ~@body) all-bindings)))

我这样称呼

(with-mocked-grpc [plans/usage-summary [:ok ^{:sized 100 :binding a} _]] 1)

我得到这个例外

CompilerException java.lang.RuntimeException: Unable to resolve symbol: a in this context, compiling:(*cider-repl plans-service/client:localhost:45691(clj)*:204:20)

check-response为该宏的使用者构建生成的值以供在测试中使用，check-binding查找用户要求绑定到变量的生成的值。

macroexpand返回

(let [a {:generated :value}] 1)

Answer 1

宏扩展后元数据仍然可以解析，因此将let行更改为

(let [~(with-meta v nil) ~(with-meta binding nil)] ~acc)

解决了。

Clojure中使用宏进行变量捕获

1 个答案: