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Compiler construction is at the heart of computer science. As I continue to make my way, if very slowly, though The Dragon Book, it is becoming absolutely clear to me that some things cannot be understood without building them. What Halmos stated so strikingly about mathematics is applicable here:

The only way to learn mathematics is to do mathematics […] The right way to read mathematics is first to read the definitions of the concepts and the statements of the theorems, and then, putting the book aside, to try to discover the appropriate proofs. If the theorems are not trivial, the attempt might fail, but it is likely to be instructive just the same. To the passive reader a routine computation and a miracle of ingenuity come with equal ease, and later, when he must depend on himself, he will find that they went as easily as they came. The active reader, who has found out what does not work, is in a much better position to understand the reason for the success of the author’s method, and, later, to find answers that are not in books. — Paul Halmos, A Hilbert Space Problem Book.

The only way to understand compilers is to build them. It is my goal, therefore, to attach a project to each chapter (or sequence of chapters) that addresses a particular topic: and for chapter 3, which is on lexical analysis, the only possible answer was an implementation of Lex.

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