Summary
This book showed you a thing or two about building programming languages. We did this by showing you an implementation of a toy language called Jzero. However, Jzero is not what is interesting; what is interesting is the tools and techniques used in its implementation. We even implemented it twice!
If you thought that maybe programming language design and implementation was a swimming pool to enjoy, your new conclusion might be that it is more like an ocean. If so, the tools that have been placed at your disposal in this book, including versions of flex and YACC for use with Unicon or Java, are a luxury cruise liner capable of sailing you about on that ocean to wherever you want to go.
The first high-level language compiler is said to have taken 18 person-years to create. Perhaps now it is a task of a few months, although it is still an open-ended task where you can spend as much time as you can spare making improvements to any compiler or interpreter that you care...