tree comparison using lua coroutines

tree.lua

#!/usr/local/bin/lua

function T(l, v, r)
	return {left = l, value = v, right = r}
end

function visit(t)
	if t ~= nil then  -- note: ~= is "not equal"
		visit(t.left)
		coroutine.yield(t.value)
		visit(t.right)
	end
end

function cmp(t1, t2)
	co1 = coroutine.create(visit)
	co2 = coroutine.create(visit)
	while true
	do
		ok1, v1 = coroutine.resume(co1, t1)
		ok2, v2 = coroutine.resume(co2, t2)
		if ok1 ~= ok2 or v1 ~= v2 then
			return false
		end
		if not ok1 and not ok2 then
			return true
		end
	end
end

function cmp2(t1, t2)
	next1 = coroutine.wrap(function() visit(t1) end)
	next2 = coroutine.wrap(function() visit(t2) end)
	while true
	do
		v1 = next1()
		v2 = next2()
		if v1 ~= v2 then
			return false
		end
		if v1 == nil and v2 == nil then
			return true
		end
	end
end

t1 = T(T(T(nil, 1, nil), 2, T(nil, 3, nil)), 4, T(nil, 5, nil))
t2 = T(nil, 1, T(nil, 2, T(nil, 3, T(nil, 4, T(nil, 5, nil)))))
t3 = T(nil, 1, T(nil, 2, T(nil, 3, T(nil, 4, T(nil, 6, nil)))))

print(cmp(t1, t2), cmp(t1, t3))
print(cmp2(t1, t2), cmp2(t1, t3))