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As an introductory text, it reads more like a summary of journal articles.

However, I would recommend chapter 2, which builds a complete compiler for a very simple language (arithmetic expressions). In the first edition, that did it in C, and it's very simple and clear. In the second edition, they did it in Java, and making it object-oriented makes it much less clear. I therefore recommend the 1st ed (plus, the hand-drawn dragon on the cover looks much better than the purple cgi dragon on the 2nd ed.)

Note that there is more than one hand-drawn dragon book cover by Aho & Ullman. Principles of Compiler Design tends to precede "The Dragon Book" as commonly referred, although the material overlaps a lot. The newer editions are much less clear with regard to the trade-offs in parser design, e.g. I don't think the section on concrete and abstract syntax uses the phrase "scannerless" or "scanner" at all while I am pretty sure PoCD at least says "scanner" and explains why you might separate the scanner/lexer from the parser. The Java book is much less clear, even though it improves on the reasoning (IIRC, pg ~113 in the Java edition) for why you should keep the two separate (although I personally consider these reasons to be myths) -- it is the fact that they don't really build up to the idea that makes me wonder why they provide justifications in the first place. They don't really debate whether concrete syntax is that useful, etc.

I have to agree that the Java code is an academic object-oriented programming example. It's not "less clear" so much as "less practical". For comparison, see the ANTLR API reference and the interfaces provided there, which differ just enough to show practical consideration for the use cases one might want.

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