'(报价单)在方案中 [英] '(quote quote) in scheme

问题描述

我正在尝试自己学习方案.谁能告诉我为什么 '(quote quote) 会输出 'quote，而 '(quote 'quote) 会输出 ''报价?

I'm trying to learn scheme by myself. Could anyone tell me why '(quote quote) will output 'quote, and '(quote 'quote) will output ''quote?

非常感谢！

推荐答案

这个表达式:

'(quote quote)

... 将 ' 展开为 (quote ) 后等价于 (quote (quote quote))code>，注意符号quote 被引用 两次，这个表达式被计算并打印为''quote.

... after expanding '<something> to (quote <something>) is equivalent to (quote (quote quote)), notice that the symbol quote is being quoted two times, and this expression is evaluated and printed as ''quote.

另一方面，这个表达式:

On the other hand, this expression:

'(quote 'quote)

...等价于(quote(quote(quote quote)))，注意符号quote被引用三个次，这个表达式被计算并打印为 '''quote.

... is equivalent to (quote (quote (quote quote))), notice that the symbol quote is being quoted three times, and this expression is evaluated and printed as '''quote.

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