From Future Plans...
> And after Volumes 1--5 are done, God willing, I plan to publish Volume 6 (the theory of context-free languages) and Volume 7 (Compiler techniques), but only if the things I want to say about those topics are still relevant and still haven't been said. Volumes 1--5 represent the central core of computer programming for sequential machines; the subjects of Volumes 6 and 7 are important but more specialized.
And about Volume 5...
> Syntactic Algorithms, in preparation.
9. Lexical scanning (includes also string search and data compression)
10. Parsing techniques
Not to forget he was asked specifically to write a book about compilers (= "Volume 7") by Addison Wesley in the 1960s.
Now, half a century later, he is chickening out...