There is an example which turns infix math expressions into sexps. Could Strucjure be used to write a Computer Algebraic System (CAS)? I would guess that most algebra is probably simpler than the Red/Black tree example.
The math that goes into making a useful CAS can be beautiful, but "simpler than red-black trees" is not a description that springs to mind. A toy CAS might be pretty easy, though.
