The usual way currently is to use a common "datatypes" file.
See also the current discussion to improve the status quo: https://forum.nim-lang.org/t/4745
will circular module dependencies be something that will be added to Nim?
Yes, eventually. I personally would like to have a submodule concept for this so that the cycle is restricted to a set of "submodules" but the last time I brought it up it didn't have many sympathizers...
Why do you think that you have to ask here and on reddit AT THE SAME TIME?
Do you expect Araq and mratsim to answer also at reddit? Or shall the reddit questions stay without a good, core dev reply, giving a bad impression about Nim?
Other location for questions may be fine when someone is not registered here, or when here really no good answer is available -- maybe AFTER some days.
https://www.reddit.com/r/nim/comments/c51has/circular_module_importing/
There is nothing wrong with asking in two places. Please don't criticize people for doing, or at least not in the way that you're doing it.
It would be nice if the author added a link to Reddit and vice versa, but otherwise there is no problem in asking in both places.