java Clojure While 循环
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Clojure While Loop
提问by Hamza Yerlikaya
I trying clojure i am trying to figure out how to implement the following algorithm,
我在尝试 clojure 我想弄清楚如何实现以下算法，
I am reading from an input stream i want to continue reading until it is not a delimiter character.
我正在从输入流中读取我想继续读取直到它不是分隔符为止。
i can do this in java with a while loop but i can't seem to figure out how to do it in clojure?
我可以在 java 中使用 while 循环执行此操作，但我似乎无法弄清楚如何在 clojure 中执行此操作？
while read readChar != delimiter do some processing.... end while
采纳答案by Nathan Shively-Sanders
I don't know Clojure, but it looks that, like Scheme, it supports "let loops":
我不知道 Clojure，但看起来像 Scheme 一样，它支持“让循环”：
(loop [char (readChar)]
(if (= char delimiter)
'()
(do (some-processing)
(recur (readChar)))))
Hope this is enough to get you started. I referred to http://clojure.org/special_forms#toc9to answer this question.
希望这足以让你开始。我参考了http://clojure.org/special_forms#toc9来回答这个问题。
NOTE: I know that Clojure discourages side-effects, so presumably you want to return something useful instead of '().
注意：我知道 Clojure 不鼓励副作用，所以大概你想返回一些有用的东西而不是 '() 。
回答by wrongusername
Working on Clojure 1.3.0, and for what it's worth, you can write while loops in Clojure now by doing something akin to
在 Clojure 1.3.0 上工作，并且为了它的价值，您现在可以通过执行类似于以下操作的方式在 Clojure 中编写 while 循环
(while truth-expression
(call-some-function))
回答by user499049
The loop approach will work fine in clojure however loop/recur are considered low level operations and higher order functions usually preferred.
循环方法在 clojure 中可以正常工作，但是循环/递归被认为是低级操作，通常更喜欢高阶函数。
Normally this sort of problem would be solved by creating a sequence of tokens (characters in your example) and applying on or more of clojure's sequence functions (doseq, dorun, take-while, etc.)
通常，这类问题可以通过创建一系列标记（您的示例中的字符）并应用一个或多个 clojure 的序列函数（doseq、dorun、take-while 等）来解决。
The following example reads the first username from /etc/passwd on unix like systems.
以下示例在类 Unix 系统上从 /etc/passwd 读取第一个用户名。
(require '[clojure.java [io :as io]])
(defn char-seq
"create a lazy sequence of characters from an input stream"
[i-stream]
(map char
(take-while
(partial not= -1)
(repeatedly #(.read i-stream)))))
;; process the sequence one token at a time
;; with-open will automatically close the stream for us
(with-open [is (io/input-stream "/etc/passwd")]
(doseq [c (take-while (partial not= \:) (char-seq is))]
;; your processing is done here
(prn c)))
回答by drewr
I came up with this in the spirit of line-seq. It's fully lazy and exhibits more of Clojure's functional nature than loop.
我本着line-seq. 它是完全惰性的，并且比loop.
(defn delim-seq
([#^java.io.Reader rdr #^Character delim]
(delim-seq rdr delim (StringBuilder.)))
([#^java.io.Reader rdr #^Character delim #^StringBuilder buf]
(lazy-seq
(let [ch (.read rdr)]
(when-not (= ch -1)
(if (= (char ch) delim)
(cons (str buf) (delim-seq rdr delim))
(delim-seq rdr delim (doto buf (.append (char ch))))))))))
满贴。
回答by jk.
A while-loop usually involves mutable variables, i.e. waiting until a variable meets a certain condition; in Clojure you'd usually use tail-recursion (which the compiler translates into a while-loop)
while 循环通常涉及可变变量，即等待变量满足某个条件；在 Clojure 中，您通常会使用尾递归（编译器将其转换为 while 循环）
The following is not quite a solution, but this variation of the for-loop might be of help in some cases:
以下不是一个很好的解决方案，但 for 循环的这种变体在某些情况下可能会有所帮助：
(for [a (range 100)
b (range 100)
:while (< (* a b) 1000)]
[a b]
)
This will create a list of all the pairs of a and b until(< (* a b) 1000). That is it will stop as soon as the condition is met. If you replace :while with :when, they you can find allof the pairs that meet the condition, even after it finds one that doesn't.
这将创建一个包含所有 a 和 b 对的列表，直到(< (* a b) 1000)。也就是说，它会在满足条件后立即停止。如果您将 :while 替换为 :when，则它们可以找到所有满足条件的对，即使在找到不满足条件的对之后也是如此。
回答by Leonardo
I came out with this version:
我推出了这个版本：
(defn read-until
[^java.io.Reader rdr ^String delim]
(let [^java.lang.StringBuilder salida (StringBuilder.) ]
(while
(not (.endsWith (.toString salida) delim))
(.append salida (str (char (.read rdr))))
)
(.toString salida)
)
)
It looks for a String, not a single char as delimiter!
它寻找一个字符串，而不是单个字符作为分隔符！
Thanks!
谢谢！
