没有表达式树的话，我们是不可能用描述格式来表示一个表达式的。他们唯一的表示方式是IL(中间语言)，这种语言对于重新表述用户的意图来说太低层次了。

Without expression trees, its impossible to describe expressions in a descriptive format; the only description of them is IL, which is too low level to re-create the user's intent for the expression.

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编译器的前端是特定于语言的，它包括一个用于给定语言的解析器，这个解析器产生经过解析的树和中间表示(Register Transfer Language, RTL)。

The front end of a compiler is language specific and includes a parser for the given language that results in parsed trees and the intermediate representation (the Register Transfer language, or RTL).

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