[_raul]

Notice that while the linked page says "You can read the whole book, for free, online", chapters 18 to 30 haven't been written yet (e.g: http://craftinginterpreters.com/types-of-values.html).

[SiempreViernes]

Slightly below the button marked "start reading" there is a section entitled "What’s the Catch?" that explains as much.

[giancarlostoro]

I was about to write that very comment. It's not like he's hiding it, and he's giving the (e)book out for free, what more could you ask?

[springogeek]

The same was true of the author's previous book, Game Programming Patterns, which is now complete and fully published.

[BalinKing]

(... and still free online!)