使用-?>;用Clojurescript?
在我的Clojure共享资源中,我有以下内容(我无耻地偷了): 在我的Clojurescript代码中,我有以下内容(I:要求宏为c) 不幸的是,当我编译时,我得到:使用-?>;用Clojurescript?,clojure,clojurescript,Clojure,Clojurescript,在我的Clojure共享资源中,我有以下内容(我无耻地偷了): 在我的Clojurescript代码中,我有以下内容(I:要求宏为c) 不幸的是,当我编译时,我得到: WARNING: Use of undeclared Var webstack.client/-?> at line 56 cljs-src/webstack/client.cljs WARNING: Use of undeclared Var webstack.client/-?> at line 57 cljs-s
WARNING: Use of undeclared Var webstack.client/-?> at line 56 cljs-src/webstack/client.cljs
WARNING: Use of undeclared Var webstack.client/-?> at line 57 cljs-src/webstack/client.cljs
WARNING: Use of undeclared Var webstack.client/-?> at line 58 cljs-src/webstack/client.cljs
当我在浏览器中打开javascript时,会出现“hey Stephen”警报对话框,但在按下“hey Stephen”警报上的“ok”后,会立即出现无处不在的“Uncaught TypeError:Cannot call method'call'of undefined”错误。果然,看看生成的javascript代码,我的js/alert变成了:
alert([cljs.core.str("hey "), cljs.core.str("Stephen")].join(""));
alert(webstack.client.__QMARK__GT_.call(null, webstack.client.__QMARK__GT_.call(null, webstack.client.a, cljs.core.first), "\ufdd0'a"));
alert(webstack.client.__QMARK__GT_.call(null, webstack.client.__QMARK__GT_.call(null, webstack.client.b, cljs.core.first), "\ufdd0'a"));
alert(webstack.client.__QMARK__GT_.call(null, webstack.client.__QMARK__GT_.call(null, webstack.client.c, cljs.core.first), "\ufdd0'a"))
很明显,我可以使用宏,但是-?>(和相关)宏的编写方式导致它们无法编译。要使用这些
-?>
和“-?>”宏,我需要做什么?可能正在创建函数,而不是宏中的另一个宏可以帮助您解决此问题:
(defmacro defnilsafe [docstring non-safe-name nil-safe-name]
`(defn ~nil-safe-name ~docstring
([x# form#]
(let [i# x#] (when-not (nil? i#) (~non-safe-name i# form#))))
([x# form# & more#]
(apply ~nil-safe-name (~nil-safe-name x# form#) more#))))
-?>在使用clojure 1.5.1和cljsbuild 0.3.0时适用,但仅当我使用:use macros而不是:require macros时适用。当我使用:require macros时,clojurescript尝试将宏解析为本地名称空间中的变量,这是不正确的。我想你在clojurescript中发现了一个bug,为什么不报告呢
(ns test.test
;(:use-macros [test.nilsafe :only [hey-str -?>]]) ;uncomment and everything works!
(:require-macros [test.nilsafe :as tn]))
(def a nil)
(def b [])
(def c [{:a 23}])
(.log js/console (tn/hey-str "Stephen")) ;; should display "hey Stephen"
(.log js/console (tn/-?> a first :a)) ;; should display nil
(.log js/console (tn/-?> b first :a)) ;; should display nil
(.log js/console (tn/-?> c first :a))
让我确信这是一个bug的是,取消注释:use宏将导致文件正确编译,即使我没有从变量中删除tn/scope。marco很简单
(defmacro ->
"Threads the expr through the forms. Inserts x as the
second item in the first form, making a list of it if it is not a
list already. If there are more forms, inserts the first form as the
second item in second form, etc."
{:added "1.0"}
[x & forms]
(loop [x x, forms forms]
(if forms
(let [form (first forms)
threaded (if (seq? form)
(with-meta `(~(first form) ~x ~@(next form)) (meta form))
(list form x))]
(recur threaded (next forms)))
x)))
写一个零安全的应该很简单(下面的例子没有经过测试),但是你得到了这个概念
(defmacro -?>
[x & forms]
(loop [x x, forms forms]
(if (and forms (some? x)) ; check nil to exit eariler
(let [form (first forms)
threaded (if (seq? form)
(with-meta `(~(first form) ~x ~@(next form)) (meta form))
(list form x))]
(recur threaded (next forms)))
x)))
您可以尝试为nil-safe名称创建一个宏(从defnilsafe宏)而不是创建一个函数吗?@Ankur否,它必须是一个宏,因为它需要在计算之前在编译/宏扩展时排列表达式。@rplevy:我说的是,该宏正在创建另一个宏,相反,宏可以创建function@Ankur你将如何编写-?>
作为函数?@Ankur这是一个反问句。正确答案是,你不能。试试(?>nil(println“hello world”)
。这与原始宏的作用不同。这怎么可能呢?@Cubic,你是对的,它不会像处理表达式那样处理函数,而是处理函数,例如:(?>nil println)
,但这不是->宏所做的,因此也不是-?>宏应该做的。
(defmacro ->
"Threads the expr through the forms. Inserts x as the
second item in the first form, making a list of it if it is not a
list already. If there are more forms, inserts the first form as the
second item in second form, etc."
{:added "1.0"}
[x & forms]
(loop [x x, forms forms]
(if forms
(let [form (first forms)
threaded (if (seq? form)
(with-meta `(~(first form) ~x ~@(next form)) (meta form))
(list form x))]
(recur threaded (next forms)))
x)))
(defmacro -?>
[x & forms]
(loop [x x, forms forms]
(if (and forms (some? x)) ; check nil to exit eariler
(let [form (first forms)
threaded (if (seq? form)
(with-meta `(~(first form) ~x ~@(next form)) (meta form))
(list form x))]
(recur threaded (next forms)))
x)))