使用迄今为止学到的东西，现在能够构建简单的计算器来计算算术表达式，如清单9所示。
Using what you have learned so far, you could now build a simple calculator to evaluate arithmetic expressions as shown in Listing 9.
如前面所述，表达式节点还支持简单的算术和逻辑表达式。
As mentioned, expression nodes also support simple arithmetic and logical expressions.
表达式节点支持包含算术和布尔(真或假逻辑)运算符的简单表达式。
Expression nodes support simple expressions involving arithmetic and Boolean (true or false logic) operators.
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