Reaktor FastTrack morse code DFA solution

build-dfa.clj

(ns test.core
    (:require [clojure.string :as str]))

(def morse 
    (into [] 
        (sort-by key (comparator (fn [x y] (<= (count x) (count y)))) 
        {".-" "A" "-..." "B" "-.-." "C" "-.." "D" "." "E" "..-." "F" "--." "G" "...." "H" ".." "I" ".---" "J" "-.-" "K" ".-.." "L" "--" "M" "-." "N" "---" "O" ".--." "P" "--.-" "Q" ".-." "R" "..." "S" "-" "T" "..-" "U" "...-" "V" ".--" "W" "-..-" "X" "-.--" "Y" "--.." "Z"})))

(defn build-dfa 
    ([codes] (build-dfa codes []))
    ([codes current-list]
     (letfn [(first-char [c codes] (filter (fn [[code letter]] (= c (first code))) codes))
             (drop-first-char [codes] (map (fn [[k v]] [(subs k 1) v]) codes))
             (build-sublist [c codes] (-> (first-char c codes) (drop-first-char)))]
        (let [[code letter] (first codes)]
          (cond (not (empty? (rest codes)))
                    (let [result-dit (build-dfa (build-sublist \. codes) current-list)
                          index-dit  (if (> (count result-dit) (count current-list)) (dec (count result-dit)) nil)
                          result-dah (build-dfa (build-sublist \- codes) result-dit)
                          index-dah  (if (> (count result-dah) (count result-dit)) (dec (count result-dah)) nil)]
                        (concat result-dah [[index-dit index-dah (if (empty? code) letter nil)]]))
                (and (not (empty? letter)) (empty? code))
                    (concat current-list [[nil nil letter]])
                :else current-list)))))

(defn dfa->javascript-array [dfa]
  (str "[" (str/join 
            "," 
            (letfn [(print-number [n] (if (number? n) n nil))
                    (print-char [n] (if (string? n) (format "'%s'" n) nil))]
                (map (fn [[dit dah letter]]
                    (format "[%s]" (str/join "," (remove nil? [(print-number dit) (print-number dah) (print-char letter)])))) dfa)))
        "]"))

(let [dfa (build-dfa morse)]
    (println
      (format (str "var morse_dfa = %s, l = %d, current_step = l, r;\n" 
              "function morse(s) {\n"
              "  if(typeof (current_step = morse_dfa[current_step][{'dit':0,'dah':1,'pause':morse_dfa[current_step].length-1}[s]]) !== 'number') {\n"
              "    r = current_step; current_step = l;\n"
              "    return r;\n"
              "  }\n"
              "}\n")
              (dfa->javascript-array dfa) (dec (count dfa)))))

morse.js

var morse_dfa = [['H'],['V'],[0,1,'S'],['F'],[3,'U'],[2,4,'I'],['L'],[6,'R'],['P'],['J'],[8,9,'W'],[7,10,'A'],[5,11,'E'],['B'],['X'],[13,14,'D'],['C'],['Y'],[16,17,'K'],[15,18,'N'],['Z'],['Q'],[20,21,'G'],['O'],[22,23,'M'],[19,24,'T'],[12,25]], l = 26, current_step = l, r;
function morse(s) {
  if(typeof (current_step = morse_dfa[current_step][{'dit':0,'dah':1,'pause':morse_dfa[current_step].length-1}[s]]) !== 'number') {
    r = current_step; current_step = l;
    return r;
  }
}