Tweaking string.gsub so it's yieldable

["Soni L." <fakedme@...>]

How can I tweak string.gsub so it's yieldable?

More specifically I want my tweaked Lua to support this:

c = coroutine.create(function() return string.gsub("test", ".", coroutine.yield) end)
for i = 1, 4 do
	print(coroutine.resume(c))
end

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