Dr Racket 与 SICP 的问题
我正在通过 SICP 进行工作。目前，在第一章中，我在让 Racket 重新定义“基元”时遇到问题。例如，我的印象是我应该能够任意执行 (define + 5) ，这样就可以了，或者重新定义 sqrt 过程。相反，我得到的是：
define-values: cannot change constant variable: +
我当前将语言设置为 R5RS，我的印象是它会解决与 SICP 的兼容性问题。
I'm working through SICP. Currently, in the first chapter, I'm having problems getting Racket to let me redefine "primitives". For instance, I was under the impression that I should be able to arbitrarily do (define + 5) and that would be fine, or redefine the sqrt procedure. Instead, I get this:
define-values: cannot change constant variable: +
I have the language currently set to R5RS, which I was under the impression would take care of the compatibility issues with SICP.
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即使可能，在没有真正了解系统对此有何反应的情况下，您也不应该进行此类重新定义。例如，如果重新定义
+，其他代码会中断吗？在 Racket 的例子中，答案是“否”——但这是因为您实际上并没有重新定义+：相反，您定义了一个新的+，只有您的代码可以使用。至于语言选择——Rackets R5RS模式是一个非常严格的模式，你通常不会想使用它。要获得对 SICP 更加友好的环境，请参阅 Neil Van Dyke 的 SICP 支持页面< /a> 将为您提供专门为本书制作的语言。 （IIRC，它甚至具有书籍展示的图形语言。）
Even if possible, such redefinitions are not something that you should do without really understanding how the system will react to this. For example, if you redefine
+, will any other code break? The answer to that in Racket's case is "no" -- but this is because you don't really get to redefine+: instead, you define a new+, which only your code can use.As for the language choice -- Rackets R5RS mode is a very strict one, and it's not something that you'd usually want to use. For a much more SICP-friendly environment, see Neil Van Dyke's SICP Support page which will provide you with a language specifically made for the book. (IIRC, it even has the graphical language that the books shows off.)
我在尝试使用此处的 RSA 示例时遇到了问题（SICP 内容的一部分）：
http://mitpress.mit.edu/sicp/psets/ps3/readme.html
为了让这个工作，我必须这样做：
1）通过将其添加到空白文件的顶部来运行初始下载：
然后点击“运行”
2）享受 DrRacket 非常用户友好的自动下载和安装PLAneT Neil 模块，去喝杯咖啡；-)
3) 安装完成后，关闭 DrRacket。
4) 重新打开，然后从选择语言列表中选择 SICP PLAneT 1.15。
（除了执行初始下载之外，我无法在顶部添加声明来为我工作。）
祝你好运！
I ran into problems trying to work thru the RSA example here (part of the SICP stuff):
http://mitpress.mit.edu/sicp/psets/ps3/readme.html
To get this working I had to do this:
1) Run thru the initial download by adding this to the top of a blank file:
and then hitting "Run"
2) Enjoy DrRacket's very user friendly, automatic download and install the PLaneT Neil module by going to grab a coffee ;-)
3) And then once it is installed, close DrRacket.
4) Reopen, and choose SICP PLaneT 1.15 from the Choose A Language list.
(I could not get adding the declaration at the top to work for me aside from doing that to perform the initial download.)
Good luck!
在语言面板中，您需要禁用“不允许重新定义初始绑定”。这解决了这个问题。
In the language panel, you need to disable "disallow redefinition of initial bindings." This fixes the issue.