def statement(type, hook, opt={})
      lang = opt[:lang] || Cog.active_language
      lang.comment_pattern("#{type}\\s*:\\s*(#{hook})\\s*(?:\\(\\s*(.+?)\\s*\\))?(\\s*once\\s*)?(?:\\s*([{]))?")
    end
def statement(type, hook, opt={})
      lang = opt[:lang] || Cog.active_language
      lang.comment_pattern("#{type}\\s*:\\s*(#{hook})\\s*(?:\\(\\s*(.+?)\\s*\\))?(\\s*once\\s*)?(?:\\s*([{]))?")
    end
Pattern groups are
 * 1 - hook
 * 2 - args
 * 3 - once
 * 4 - expansion begin (curly <tt>{</tt>)
 @return [Regexp] pattern to match the beginning of a cog embed statement