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DSL 执行的几种模式：

1. 作为 script 直接运行（比如 AWK）
2. 作为 bytecodes 在 VM 之上运行（比如 JAVA 系的DSL）
3. 作为编译器时的元语言运行（比如 Lisp）
The script can directly execute the underlying model without any more code generation or manipulation.

 There might be an interpreter that directly interprets the script and runs it. The UNIX little programming languages awk and sed are examples of DSLs that execute directly.
A DSL script that’s developed on a virtual machine follows the second model.

The semantic model underlying any Java DSL script generates bytecodes that
are executed on the JVM.
Some languages offer compile-time metaprogramming.

 When you’re developing a DSL using this kind of language, you build metastructures as part of your source code, which get translated to the normal forms of the language before it runs.

 Lisp supports this technique through macros that get expanded to normal Lisp forms during the macro expansion phase (I discuss this in more
detail in appendix B). 

For these languages, there’s an intermediate stage where you have source code translation before the byte code is generated for the virtual machine.