The single quotation mark in front of the null list is used to tell Scheme that you are using as data and not as a part of your parse tree.

空列表前面的单引号用来告诉scheme您正在使用作为数据，而不是用它作为解析树的一部分。

youdao

I used this product my entire pregnancy, almost every day. I did not have a single stretch mark the entire time.

整个怀孕期间，几乎每天使用这个产品，没有出现过一条妊娠纹。

youdao

Not a single song hits the four-minute mark.

NPR: The High Strung: 'Real Stone'