html_characters.ex

defmodule HTMLCharacters do

  def sanitize(phrase) do
    chars = %{"&quot;" => "\"", "&#39;" => "'", "&amp;" => "&", "&lt;" => "<", "&gt;" => ">"}

    cond do
      String.match?(phrase, ~r/&\#?.+;/) -> 
        [code] = Regex.run(~r/&\#?.+;/, phrase)
        Regex.replace(Regex.compile!(code), phrase, chars[code])
      true -> phrase
    end
  end
end