问题
I'm trying to learn scheme by myself. Could anyone tell me why '(quote quote) will output 'quote, and '(quote 'quote) will output ''quote?
Thank you very much!
回答1:
This expression:
'(quote 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.
On the other hand, this expression:
'(quote '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.
回答2:
Take a look at (free, online) How To Design Programs, intermezzo 2. It explains quote in terms of list and cons. If anything in that explanation doesn't make sense, just back up a bit in the textbook.
来源：https://stackoverflow.com/questions/12520835/quote-quote-in-scheme