Those defines remind me of how Bourne shell was originally written using such a system to make the source look more like Algol 68. It might even still be maintained that way in BSD to this day [0].
"to this day" in 1994 is very much not "to this day" in 2020.
The various BSDs use the Almquist and Korn shells for /bin/sh nowadays. Indeed, M. Van der Linden was out of date even back in 1994. At that time, BSD had already been largely freed of AT&T code, such as the Bourne shell, for 3 years. It's now approaching 3 decades.
[0] https://books.google.ca/books?id=9f9uAQAAQBAJ&pg=PA9&lpg=PA9...