nested-parser.clj

(ns nested-parser
  (:require [clojure.string :as str]))

(defmacro parse-symbol
  [s v]
  (let [n `(name ~s)
        lvls `(map keyword (str/split ~n #"\."))]
    `(assoc-in {} ~lvls ~v)))

(parse-symbol 'foo.bar.baz 1)
;; => {:foo {:bar {:baz 1}}}

(defn nested-merge
  [m1 m2]
  (if (and (map? m1) (map? m2))
    (merge-with nested-merge m1 m2)
    m2))

(defn parse-nested
  [m]
  (reduce
   (fn [acc [s v]]
     (nested-merge acc (parse-symbol s v)))
   {}
   m))

(parse-nested
 {'foo.bar.baz 1
  'foo.baz 2
  'foo.bar.bim 3})
;; => {:foo {:bar {:baz 1, :bim 3}, :baz 2}}