I'm not sure why this is linked. This online toplevel is very old.
People who want a more modern version, with more exercises should follow the online MOOC [1] or use this website [2].
People who just want an online OCaml/Reason interpreter to play with should use https://sketch.sh/ml
1: https://www.fun-mooc.fr/courses/course-v1:parisdiderot+56002...