V dict_fname = ‘unixdict.txt’

F load_dictionary(String fname = dict_fname)
   ‘Return appropriate words from a dictionary file’
   R Set(File(fname).read().split("\n").filter(word -> re:‘[a-z]{3,}’.match(word)))

F get_players()
   V names = input(‘Space separated list of contestants: ’)
   R names.trim(‘ ’).split(‘ ’, group_delimiters' 1B).map(n -> n.capitalize())

F is_wordiff_removal(word, String prev; comment = 1B)
   ‘Is word derived from prev by removing one letter?’
   V ans = word C Set((0 .< prev.len).map(i -> @prev[0 .< i]‘’@prev[i + 1 ..]))
   I !ans
      I comment
         print(‘Word is not derived from previous by removal of one letter.’)
   R ans

F counter(s)
   DefaultDict[Char, Int] d
   L(c) s
      d[c]++
   R d

F is_wordiff_insertion(String word, prev; comment = 1B) -> Bool
   ‘Is word derived from prev by adding one letter?’
   V diff = counter(word)
   L(c) prev
      I --diff[c] <= 0
         diff.pop(c)
   V diffcount = sum(diff.values())
   I diffcount != 1
      I comment
         print(‘More than one character insertion difference.’)
      R 0B

   V insert = Array(diff.keys())[0]
   V ans = word C Set((0 .. prev.len).map(i -> @prev[0 .< i]‘’@insert‘’@prev[i ..]))
   I !ans
      I comment
         print(‘Word is not derived from previous by insertion of one letter.’)
   R ans

F is_wordiff_change(String word, String prev; comment = 1B) -> Bool
   ‘Is word derived from prev by changing exactly one letter?’
   V diffcount = sum(zip(word, prev).map((w, p) -> Int(w != p)))
   I diffcount != 1
      I comment
         print(‘More or less than exactly one character changed.’)
      R 0B
   R 1B

F is_wordiff(wordiffs, word, dic, comment = 1B)
   ‘Is word a valid wordiff from wordiffs[-1] ?’
   I word !C dic
      I comment
         print(‘That word is not in my dictionary’)
      R 0B
   I word C wordiffs
      I comment
         print(‘That word was already used.’)
      R 0B
   I word.len < wordiffs.last.len
      R is_wordiff_removal(word, wordiffs.last, comment)
   E I word.len > wordiffs.last.len
      R is_wordiff_insertion(word, wordiffs.last, comment)

   R is_wordiff_change(word, wordiffs.last, comment)

F could_have_got(wordiffs, dic)
   R (dic - Set(wordiffs)).filter(word -> is_wordiff(@wordiffs, word, @dic, comment' 0B))

V dic = load_dictionary()
V dic_3_4 = dic.filter(word -> word.len C (3, 4))
V start = random:choice(dic_3_4)
V wordiffs = [start]
V players = get_players()
V cur_player = 0
L
   V name = players[cur_player]
   cur_player = (cur_player + 1) % players.len

   V word = input(name‘: Input a wordiff from '’wordiffs.last‘': ’).trim(‘ ’)
   I is_wordiff(wordiffs, word, dic)
      wordiffs.append(word)
   E
      print(‘YOU HAVE LOST ’name‘!’)
      print(‘Could have used: ’(could_have_got(wordiffs, dic)[0.<10]).join(‘, ’)‘ ...’)
      L.break