Common Lisp has return-from; is there any sort of return in Clojure for when you want to return early from a function?
return-from
return
The if option already given is probably the best choice, and note since maps are easy, you can always return {:error "blah"} in the error condition, and{result: x} in the valid condition.
if
{:error "blah"}
{result: x}