still_not_idiomatic.cljs

(defn f [x]
  (vec (repeat (rand-int 5) [x])))

(defn g []
  (-> []
      (into ["begin"])
      (into (apply concat (for [i [\a \b \c]]
                               (f i))))
      (into ["end"])))
    
;; a little bit better
(defn g2 []
  (-> []
      (conj "begin")
      (into (reduce into (for [i [\a \b \c]]
                              (f i))))
      (conj "end")))

Someone suggested elsewhere: (conj (into ["begin"] (mapcat f [\a \b \c])) "end")

I think this does a better job of expressing the intent of the function, in so far as I understand what you are trying to do:

(defn g []
  (cons "begin" (conj (into [] (mapcat f [\a \b \c])) "end")))

Note that this version returns a lazy sequence, whereas yours returns a vector. Not sure if that matters to you or not, but you should be aware of lazy vs. non-lazy for such things so that you don't get bitten without knowing it. You could take the code I posted and thread it if you wanted, depending on what the real code will be doing. But that's just syntactical sugar, for the most part.

Yeah, I want to get a vector for hiccup out of that. Thanks for your input!