-module(word_count).
-export([count/1]).

-spec count(string()) -> dict:dict(string(), integer()).
count(S) ->
  lists:foldl(fun (K, Acc) -> dict:update_counter(K, 1, Acc) end,
              dict:new(),
              tokenize(string:to_lower(S))).

is_alnum(C) ->
  (C >= $a andalso C =< $z) orelse (C >= $0 andalso C =< $9).

is_sep(C) ->
  not is_alnum(C).

tokenize([]) ->
  [];
tokenize(S) ->
  case lists:splitwith(fun is_alnum/1, lists:dropwhile(fun is_sep/1, S)) of
    {[], Rest} ->
      tokenize(Rest);
    {Word, Rest} ->
      [Word | tokenize(Rest)]
  end.