I once looked - briefly - at building an independent
TeX
implementation.
It wasn't really possible. There are pieces of TeX for which existing
documentation, at least at the time (meaning, the TeXBook) was
insufficient. Consider, for example, the "Interwoven alignment
But the TeXbook is not all the documetation. It's Volume A of a 5-volume
set ('Computers and Typesetting'), the other volumes being
B : TeX : The Program (the Woven source of TeX)
C : THe MetaFont book (user manual to MetaFont)
D : MetaFont : THe Program (the Woven source of MetaFont)
E : THe COmputer Modern Typefaces (the font source)
I would guess you'd need to read and understnad Volume B as well...
-tony