(s/and (s/keys ...) #(xor ... %))

Not that xor is a thing, but you get the idea

A concrete example from our codebase @stand

(s/def :criteria/general (s/and (s/keys :req-un [(or :criteria-item/value :criteria-item/values)
                                                 :criteria-item/weight])
                                #(not (and (:value %) (:values %)))))

A general criteria map must have :weight but can only have one of :value or :values.

I don't believe that would work in my case. I need a situation where neither :value or :values need appear but if one appears the other cannot. I don't think you can do an or in a keys :opt, can you?

Ah, no, you cannot.

But they would both just be :opt keys and you could still s/and the check that they are not both present

like this

(s/def :criteria/general (s/and (s/keys :opt-un [:criteria-item/value :criteria-item/values
                                                 :criteria-item/weight])
                                #(not (and (:value %) (:values %)))))

That would work for the neither case, the either case, and prevent the both case I think?