java - 如何从 Java 调用 Clojure 宏？

Question

有没有办法从 Java 调用 Clojure 宏？

这是我正在尝试做的事情:

RT.var("clojure.core", "require").invoke(Symbol.create("clojure.contrib.prxml"));
Var prxml = RT.var("clojure.contrib.prxml", "prxml");
Var withOutStr = RT.var("clojure.core", "with-out-str");
String stringXML = (String) withOutStr.invoke((prxml.invoke("[:Name \"Bob\"]")));

prxml 默认写入 *out*，这就是为什么我需要用返回字符串的宏 with-out-str 包装它。

我收到这个错误:

 [java] java.lang.IllegalArgumentException: Wrong number of args (1) passed to: core$with-out-str
 [java]     at clojure.lang.AFn.throwArity(AFn.java:437)
 [java]     at clojure.lang.RestFn.invoke(RestFn.java:412)
 [java]     at clojure.lang.Var.invoke(Var.java:365)
 [java]     at JavaClojure.xml.main(Unknown Source)

Answer 1

你必须自己动手做 withOutStr。

class YourClass {
    static final Var withBindings = RT.var("clojure.core", "with-bindings*");
    static final Var list = RT.var("clojure.core", "list*");
    static final Var out = RT.var("clojure.core", "*out*");
    static final Var prxml = RT.var("clojure.contrib.prxml", "prxml");

    static String withOutStr(IFn f, Object args...) {
        StringWriter wtr = new StringWriter();
        withBindings.applyTo(list.invoke(RT.map(out, wtr), f, args));
        return wtr.toString();
    }

    ...

    String stringXML = withOutStr(prxml, "[:Name \"Bob\"]");
}