Hmm, I don't think this is correct.  Reversing a `Located` thing might result in a thing with a different location.  *e.g.* see the definition of `reverseLocLine` here: https://github.com/diagrams/diagrams-lib/blob/master/src/Diagrams/Trail.hs#L868 .  The idea is that the new location is what used to be the *end* (so overall the located thing "stays in the same place"). Concretely, the idea would be to compute the offset of the underlying parametric thing (by subtracting `atStart` from `atEnd`) and to add that to the point `p` to obtain the new location. I am not 100% confident all the types will work out, but I think they should.  Let me know if you run into trouble.