当通过列表发送时，Clojure的funcs似乎没有按预期工作(Clojure's funcs don't seem to work as expected when sent t

当通过列表发送时，Clojure的funcs似乎没有按预期工作(Clojure's funcs don't seem to work as expected when sent thru a list)

在Clojure REPL中，这个表达式

( #(for [x %] (+ 100 (second x))) ['(+ 38) '(+ 48)] )

如预期的那样产生（138 148）

但是这个

( #(for [x %] ((first x) 100 (second x))) ['(+ 38) '(+ 48)] )

产生（38 48），这似乎很奇怪。

这两个表达式真的应该产生相同的结果！ 我错过了什么？ 将欣赏任何想法来解决这个谜。

顺便说一句，我试着用'apply（first x）'并将其余的参数打包到一个列表中，但它似乎并不重要。 同样的意外结果又回来了。

另外，为了验证+确实可以从输入中解析出来，我给了REPL以下内容

( #(for [x %] (resolve (first x) )) '((+ 38) (+ 48)) )

其中产生

(#'clojure.core/+ #'clojure.core/+) as expected.

At the Clojure REPL, this expression

( #(for [x %] (+ 100 (second x))) ['(+ 38) '(+ 48)] )

produces (138 148) as expected

but this

( #(for [x %] ((first x) 100 (second x))) ['(+ 38) '(+ 48)] )

produces (38 48) which seems truly weird.

Both expressions really should be producing the same result! What am I missing? Will appreciate any ideas to resolve this mystery.

BTW, I tried to use 'apply (first x)' and package the rest of the args into a list but it doesn't seem to matter. The same unexpected result comes back.

Also, to verify that the + indeed gets resolved from the input, I gave the following to the REPL

( #(for [x %] (resolve (first x) )) '((+ 38) (+ 48)) )

which produced

(#'clojure.core/+ #'clojure.core/+) as expected.

最满意答案

( #(for [x %] ((first x) 100 (second x))) ['(+ 38) '(+ 48)] )

在这里+是一个符号，而不是一个函数，因为它已经在列表中引用。 但是，符号被定义为在作为函数调用时进行地图查找（与关键字相同）。 所以('+ 100 38)和(get 100 '+ 38) 。 最后一个论点是“如果在地图中找不到我想要的东西，请返回”。 由于100不是地图，所以+使用该参数作为返回值。

为了让它做你想做的事情，你有两个选择：

使用矢量而不是引用列表可以确保+得到适当的解决。

( #(for [x %] ((first x) 100 (second x))) [[+ 38] [+ 48]] )

自己解决它，以确保您使用+功能而不是+符号。

( #(for [x %] ((resolve (first x)) 100 (second x))) ['(+ 38) '(+ 48)] ) ( #(for [x %] ((first x) 100 (second x))) ['(+ 38) '(+ 48)] )

In this the + is a symbol, not a function, because it has been quoted in the list. However, symbols are defined as doing map lookup when invoked as a function (the same as keywords). So ('+ 100 38) is the same as (get 100 '+ 38). That last argument is the "if you can't find what I want in the map, return that". Since 100 is not a map, + uses that argument as the return value.

To make it do what you want you have two options:

Use vectors instead of quoted lists ensures that + gets resolved appropriately.

( #(for [x %] ((first x) 100 (second x))) [[+ 38] [+ 48]] )

Resolve it yourself to ensure that you use the + function instead of the + symbol.

( #(for [x %] ((resolve (first x)) 100 (second x))) ['(+ 38) '(+ 48)] )