为什么Clojure会认为它应该只有一个参数？ [英] Why does Clojure recur think it should only have one argument?

问题描述

编辑：

这个问题的答案是我正在查看函数，而不是循环参数。

The answer to this is I was looking at the function, not loop parameters.

在下面两个函数的第二个，我不知道为什么recur认为它只是传递一个参数。

In the second of the following two functions, I cannot figure out why the recur thinks it so only supposed to be passed one argument.

CompilerException java.lang.IllegalArgumentException：错误的参数计数重复，期望：1 args，got：2，编译：（/ home / cnorton / projects / clojure / clj_in_action / mr1 / src / mr1.clj：84）

CompilerException java.lang.IllegalArgumentException: Mismatched argument count to recur, expected: 1 args, got: 2, compiling:(/home/cnorton/projects/clojure/clj_in_action/mr1/src/mr1.clj:84)

我没有看到什么不正确。

I am not seeing what is incorrect.

(defn determine-rover-move
    [rover-coord mov]

    (println rover-coord mov)
    (cond
        (= \L mov) (assoc rover-coord 0 (adj-compass-posL (first rover-coord)))
        (= \R mov) (assoc rover-coord 0 (adj-compass-posR (first rover-coord)))
        (= \M mov) (mov-rover rover-coord)

    ))


(defn execute-each-move
    [moves rover-coord]
    (loop [mov moves]
        (if (nil? mov)
            rover-coord
            (recur (rest moves) (determine-rover-move rover-coord mov)))))

推荐答案

重要的是这里的部​​分：

The important part is the section here:

(loop [mov moves] ...)

code> mov 到移动。虽然 recur 在循环内，因此 recur 根据 loop 定义，只有一个参数。

This code fragment is binding mov to moves from the outer function scope. The use of recur comes inside the loop though, so recur expects only one parameter according to the loop definition.

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