See here for a concrete syntax for 101companies.
Find a suitable technology/approach for lexing: Lex, Flex, Perl, Python, Handwritten, … (please find more).
ANTLR is tabu because it was covered in the lecture, but please use it for inspiration.
You do not need to deal with 101companies; please feel free to pick another interesting input format.
Produce a token sequence for companies (or some other input).
Try to put to work specifics of the lexing technology that you picked.
Prepare a short high-level presentation of your approach.