Merge sort in Clojure
I tested with a couple of input values and for the most part, it seem
fine.  Note however, that the standard sort also works with
e.g. [1 nil] (with output [nil 1]) whereas this code breaks with an
exception during the comparison.

Code looks fine with a few minor issues:


The name should be merge-sort; rsort is not meaningful.
The values (first slh) and (first srh) are written down twice; the
compiler might optimise that away, but IMO it would be nicer to have a
separate let for them.
Emacs' clojure-mode indents the :else branch differently, dunno
about that.


Some suggestions:


Support the same signature as the standard sort.
Add a docstring explaining the function.
Add tests, possibly with randomised input as well.