clojure.core.reducers/flatten

function

since v0.0-1236

(flatten)

(flatten coll)

Source docstring:

Takes any nested combination of sequential things (lists, vectors,
  etc.) and returns their contents as a single, flat foldable
  collection.

Source code @ clojurescript:src/main/cljs/clojure/core/reducers.cljs

(defcurried flatten
  {}
  [coll]
  (folder coll
   (fn [f1]
     (fn
       ([] (f1))
       ([ret v]
          (if (sequential? v)
            (-reduce (flatten v) f1 ret)
            (f1 ret v)))))))