在 Brainfuck 中实现控制结构
对于外行来说，Brainfuck 是一种图灵完备的语言，只有 8 个命令，所有命令都有C 中的字面等价物：
bf c
----------------------
> ++ptr;
< --ptr;
+ ++*ptr;
- --*ptr;
. putchar(*ptr);
, *ptr=getchar();
[ while (*ptr) {
] }
在任何具有程序包管理器的 Linux 发行版上，您应该能够找到并安装包 beef，这是一个 Brainfuck 解释器，这样您就可以在家玩了。
正如您在上面所看到的，Brainfuck 只有一个控制结构，[…] 翻译成 C 为：
while (*ptr) { … }
它为您提供了 IF VAR = 0 的所有控制然后从 BASIC 转到 10。以下代码将调用 getchar() 直到返回 0：
, # *ptr = getchar();
[ # while (*ptr) {
>, # *(++ptr) = getchar();
] # }
但是如果我只想读取换行符 \n 该怎么办？在我绞尽脑汁思考如何将其调整为简单的 if 后，我想出了以下方法：（
, # *ptr = getchar(); /* store input */
---------- # *ptr -= 10; /* test for \n by subtracting 10 before loop */
[ # while (*ptr) { /* if *ptr == 0, last char read was \n */
++++++++++ # *ptr += 10; /* wasn't \n, add 10 back to val under ptr */
>, # *(++ptr) = getchar();
---------- # *ptr -= 10;
] # }
如果有人有更好的方法，请告诉我）
现在假设除了 \n 之外，我还想在 \r 上测试跳出该循环。鉴于我只有一次机会跳出循环，我该如何测试其中任何一个？我的目标是能够模拟 switch、嵌套 if 或 if/else if。
For the uninitiated, Brainfuck is a Turing-complete language with only 8 commands, all of which have literal equivalents in C:
bf c
----------------------
> ++ptr;
< --ptr;
+ ++*ptr;
- --*ptr;
. putchar(*ptr);
, *ptr=getchar();
[ while (*ptr) {
] }
On any linux distro that has a package manager, you ought to be able to find and install the package beef, a Brainfuck interpreter so you can play along at home.
As you can see above, Brainfuck has but one control structure, […] which translates to C as:
while (*ptr) { … }
Which gives you all the control of IF VAR = 0 THEN GOTO 10 from BASIC. The following will call getchar() until it returns 0:
, # *ptr = getchar();
[ # while (*ptr) {
>, # *(++ptr) = getchar();
] # }
But what if I only want to read to a newline char \n? After having some difficulty wrapping my brain around how this could be adapted to work as a simple if I came up with the following:
, # *ptr = getchar(); /* store input */
---------- # *ptr -= 10; /* test for \n by subtracting 10 before loop */
[ # while (*ptr) { /* if *ptr == 0, last char read was \n */
++++++++++ # *ptr += 10; /* wasn't \n, add 10 back to val under ptr */
>, # *(++ptr) = getchar();
---------- # *ptr -= 10;
] # }
(If anyone has a better way of doing this, please let me know)
Now lets say I want to test break out of that loop on \r in addition to \n. How can I test for either, given that I only have one opportunity to break out of the loop? My goal is to be able to emulate switch, nested ifs or if/else ifs.
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这里是为 Brain F*ck 执行基本逻辑但复杂操作的算法:)
Here are algorithms to perform basic LOGICAL but complex operation for Brain F*ck :)
我还没有看链接，但我想 AShelly 的答案 可能更普遍有用...但是，之前不敢让我的手指输入一些 Brainfuck，我决定现在是最好的时机，并且能够得到以下内容，我< em>认为有效。
后半部分仅用于打印第一部分捕获的内容。另外，我不会说谎，在尝试解决这个问题后，我的大脑确实感觉彻底“操蛋”了……一种命名非常恰当的语言，呵呵。
I didn't take a look at the link yet, but I imagine that AShelly's answer is probably more universally useful...however, having not dared to let my fingers type out some Brainfuck before, I decided that now was as good of a time as any and was able to get the following, which I think works.
The second half is just for printing out what was captured by the first part. Also, I won't lie, my brain does indeed feel thoroughly "fucked" after having tried to work this out...A very aptly-named language, heh.
有关如何从单个 BF 控制结构开始并定义一系列的说明，请参阅此页面代表更复杂操作的日益复杂的序列。
See this page for a description of how to start with the single BF control structure and define a series of increasingly complex sequences representing more sophisticated operations.