Initially I was thinking of just playing around with M4, but that is kind of boring haha. Maybe a lisp? C? Awk+sed haha.
Just looking for a fun holiday project
EDIT: Here are a few I stumbled across the other day that I thought were pretty neat:
https://github.com/datagrok/makebakery http://m4-bloggery.invergo.net/fossil/home
FWIW, I wrote a static site generator [0] in Perl and in Python. Both are single file programs that generate the same output given the same input, which was a challenge in itself.