求值过程类似于手工计算：如果表达式中包含括号，先求嵌套最深的括号对中的子表达式的值。

The process of evaluation is similar to calculating by hand: while the expression contains parentheses, the subexpression inside the deepest nested pair of parentheses is evaluated.

youdao

请注意，您可以在子表达式中直接使用上下文，而无须使之成为另一个表达式的一部分。

Notice that you can use the context directly in a sub-expression, without necessarily making it part of another expression. The result is.

youdao

首先，请注意这个子表达式本身由两个子表达式组成，两者之间的字符并不属于任何一方。

First notice that this subexpression is itself composed of two child subexpressions, with some stuff in the middle that is not part of any child subexpression.

youdao

x It says, take the name x and create a binding for that name to the value of the sub-expression and in fact to do this, to stress a point, let's do that.

它的意思是，创建了一个名字,然后创建了对于这个名字,和子表达式的值的绑定,实际上这么做，我们是为了，要强调一个点，让我们来说说这个点。

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