verbose use of s/conform

conform.clj

(s/def ::button-template (s/cat :text string? :link (s/spec ::mb/link)))
(s/def ::button-attachment (s/keys :req [::action/text ::mb/link]))

(s/def ::button-ish (s/or ::button-template ::button-template
                          ::button-attachment ::button-attachment))

(defmulti ->button-attachment (fn [b]
                                {:pre [(s/valid? ::button-ish b)]}
                                (first (s/conform ::button-ish b))))
(defmethod ->button-attachment ::button-attachment [b] b)
(defmethod ->button-attachment ::button-template [[text link]]
  {::action/text text ::mb/link link})

(->button-attachment {::action/text "hi" ::mb/link [:link]})
(->button-attachment ["hi" [:link]])
(->button-attachment "hi")