Question

对于练习，我已经定义了

(defmacro quote-paren
  "body -> `(body)"
  [& body]
  `(~@body))

具有预期的转换(quote-paren body) =＆gt; ``（体）`。它似乎满足了一些基本测试：

user=> (macroexpand-1 `(quote-paren 3 4 5))
(3 4 5)
user=> (macroexpand-1 `(quote-paren println "hi"))
(clojure.core/println "hi") 
user=> (macroexpand-1 `(quote-paren (println "hi")))
((clojure.core/println "hi"))

但是，我一直用这个do-while宏测试它（从here修改）：

(defmacro do-while
  [test & body]
  (quote-paren loop [] 
    ~@body
    (when ~test
      (recur))))

(def y 4)
(do-while (> y 0)
  (def y (dec y)))

但结果是

IllegalStateException Attempting to call unbound fn: #'clojure.core/unquote-splicing  clojure.lang.Var$Unbound.throwArity (Var.java:43)

我不明白这一点，因为我可以看到`quote-paren'宏工作得很好（〜@ body插入）：

user=> (macroexpand-1 
         `(quote-paren loop [] 
            (def y (dec y))
            (when ~test
              (recur))))

(clojure.core/loop [] (def user/y (clojure.core/dec user/y)) (clojure.core/when #<core$test clojure.core$test@1f07f672> (recur)))

但是尝试宏扩展do-while会导致“unbound fn”。我有什么微妙的东西吗？

Answer 1

在quote-paren

之前缺少语法引用

user> (defmacro do-while
  [test & body]
  `(quote-paren loop [] 
    ~@body
    (when ~test
      (recur))))
#'user/do-while

然后正确扩展：

user> (macroexpand '(do-while (> y 0)
                      (def y (dec y))))
(loop* [] (def y (dec y)) (clojure.core/when (> y 0) (recur)))

似乎有效：

user> (def y 4)
#'user/y
user> (do-while (> y 0)
  (def y (dec y)))
nil
user>

麻烦的clojure引用-paren`（...）宏

1 个答案: