Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
This card can attack 1 additional time during the same Battle Phase for each "Chain Thrasher" in your Graveyard.
--チェイン・スラッシャー
--Chain Thrasher
local s,id=GetID()
function s.initial_effect(c)
	--multiattack
	local e1=Effect.CreateEffect(c)
	e1:SetType(EFFECT_TYPE_SINGLE)
	e1:SetCode(EFFECT_EXTRA_ATTACK)
	e1:SetValue(s.val)
	c:RegisterEffect(e1)
end
function s.val(e,c)
	return Duel.GetMatchingGroupCount(Card.IsCode,e:GetHandlerPlayer(),LOCATION_GRAVE,0,nil,id)
end