[kmeisthax]

Right, but I can think of a few cases where one might want to be generic over effect systems; especially in library code. For example, you could have a parsing library that accepts both blocking and non-blocking I/O streams. You need a Map/Then trait in order to express that generically.

[burntsushi]

I didn't say there weren't any use cases. Of course there are use cases.

I'm not even taking a side here in this thread (although I have advocated against functors/monads in the past). I'm saying that your comment is missing the point of folks who are skeptical of things like functors and monads.