finished exercises for fold-left and fold-right, but I'd prefer havign done it without flatten
ex 2.40
ex 2.42
8-queens problem working; still want to figure out how to reframe it like the book's scaffolding, and write ascii display function
adding ascii display of the generated board
finished 8-queens problem (2.42), but still want code review and to figure out what's up with the odd #<void> printing. Also finished 2.43