Summon Creature script

[Dankoo]

:}

I have an event on my OT, where players weren't suppose to summon monsters and trow magic wall runes.

I've added one protection for magic wall, by adding this in it's script:

function onCastSpell(cid, var) 
 local fromPosition = {x = 32079, y = 32206, z = 6} -- top left cornor of the playground
 local toPosition = {x = 32124, y = 32256, z = 6	} -- bottom right cornor of the playground
  if isInArea(getThingPosition(cid), fromPosition, toPosition) then
          return false, doPlayerSendCancel(cid, "You're not allowed to use it here.")
 end
        return doCombat(cid, combat, var) 
end

But the summon creature spell isn't a script, but a function:

	<instant name="Summon Creature" words="utevo res" lvl="1" params="1" exhaustion="2000" needlearn="0" event="function" value="summonMonster">
		<vocation id="1"/>
		<vocation id="2"/>
		<vocation id="5"/>
		<vocation id="6"/>
	</instant>

How can I add something similar to that code to block that specific spell in a area?

Thanks ^_^