It is not a book for compiler principle, it is a book for science theory behind the compiler principle. I have ever got a chance to create a compiler. When I was creating productions, some constraints confused me, I failed to find an answer from compiler books like dragon book. But this book resolved my problem. To be careful to read every line of this book, the book is thin so that every line is important. The book give all preliminary before a theory is introduced. But I didn't know it is important to understand following things and just ignored it. When I met the theory, I was stunned.