spec uses single map as argument with :ret and :args keys, I think it’s more clear to use positional args instead, e.g. the guard function is of type args ret -> boolean.

why? less things to remember (the keys in the map) + easier to destructure:

;; spec
(fn [{:keys [args ret]})
  (< (first args) ret))

;; proposal for malli
(fn [[arg] ret]
  (< arg ret)

ok, it needs to be arity1, so:

;; spec
(fn [{:keys [args ret]})
  (< (first args) ret))

;; proposal for malli
(fn [[[arg] ret]]
  (< arg ret)