heterogeneous async/alts?

[Peter Fraenkel]

I was hoping I could call alts! on an HVec of channels, and then match on the return value, like this:

(defn foo []

  (t/let [c-in :- (ta/Chan t/Int) (chan)

          c-in2 :- (ta/Chan t/Int) (chan)

          c-in3 :- (ta/Chan t/Str) (chan)

          tt    :- (ta/Chan (t/Val nil)) (timeout 1000)

          ]

    (ta/go-loop []

      (let [[c v] (async/alts! [c-in c-in2 c-in3 tt])]

        (case c

         c-in    (println v "is an integer")

         c-in2   (println v "is an integer")

         c-in3   (println v "is a string")

         tt      (println "Hurry up.")))

     )

  c-in))

This only type-checks if I comment out c-in3 and tt.  Ideally, it would have returned a union type of the possible return values, which would be winnowed down based on the case match.  Is this supposed to be possible?