(defn compute-count [counts char]
    (assoc counts char (inc (counts char 0))))

(defn char-count [str]
    (reduce compute-count {} str))

(char-count "Cool stuff here.") => {\space 2, \C 1, \e 2, \f 2, \h 1, \l 1, \. 1, \o 2, \r 1, \s 1, \t 1, \u 1}