Example bar item that uses data from mpd_events.lua (https://github.com/tomoe-mami/weechat-scripts/tree/master/mpd_events)

mpd_bar_item.lua

w, script_name = weechat, "mpd_bar_item"

info = {}

function item_cb()
   local symbols = { play = "▶", pause = "▮▮", stop = "■" }
   info.playback_state = symbols[info["status.state"]]

   local fmt = "MPD${color:bar_delim}: "
   local flags = {
      { "repeat", "REP" },
      { "random", "RND" },
      { "single", "SNG" },
      { "consume", "CON" }
   }

   for i, f in ipairs(flags) do
      local color = info["status."..f[1]] == "1" and "lightgreen" or "darkgray"
      fmt = fmt.."${color:"..color.."}"..f[2].." "
   end

   fmt = fmt.."${color:bar_delim}${playback_state} ${song.time}${color:bar_fg} "
   if info["song.id"] then
      if not info["song.artist"] or not info["song.title"] then
         fmt = fmt.."${song.basename}"
      else
         fmt = fmt.."${song.artist} ${color:bar_delim}-${color:bar_fg} ${song.title}"
      end
   else
      fmt = fmt.."Not playing"
   end
   return w.string_eval_expression(fmt, {}, info, {})
end

function hsignal_cb(_, _, data)
   if data.events:match(",song_changed,") or
      data.events:match(",state_[^,]+,") or
      data.idle_subsystems:match(",options,") then
      info = data
      w.bar_item_update(script_name)
   end
   return w.WEECHAT_RC_OK
end

w.register(script_name, "singalaut", "0.1", "WTFPL",
           "Example of bar item that uses data from mpd_events.lua script",
           "", "")

info = w.info_get_hashtable("mpd_events_data", {})
w.hook_hsignal("mpd_events", "hsignal_cb", "")
w.bar_item_new(script_name, "item_cb", "")