stream-file-lines-with-closing

(require '[clojure.java.io :as io]
         '[clojure.string :as str])

(defn each-line
  "Calls f with each line of a UTF-8 file, closing the reader afterwards."
  [path f]
  (with-open [rdr (io/reader (io/file path) :encoding "UTF-8")]
    (doseq [line (line-seq rdr)]
      (f line))))

(defn count-non-blank [path]
  (let [n (atom 0)]
    (each-line path (fn [line] (when-not (str/blank? line) (swap! n inc))))
    @n))