Thinking about this typesetter C may have been later
with ditroff.
No.
What I remember, there was first roff written in assembler. It was
then rewrittn into C (but now with real macro capabilities. roff
has a lt build in), Typesetter C appeared in Edition 6.1 (of 6.2)
since the n/troff code demanded a lot from the C-compiler. To make
it possible to run it on a pdp11 there was the hack turning data
into test (for the hyphenation tables). Ditroff was done by bwk
to be devie independent.
Regards,
jaap