> why don't you like this solution ? is it because it is slow ? ugly ?

I think your solution gives me the feeling that there must be something
simpler than that.

This is not criticizing you, it is rather a question to the Caml people,
like e.g. X. Leroy and colleagues and/or the ExtLibs:

(Why?) is there no really simple way getting the print functionality of
the standard toplevel?

Cheers,
Wolfgang