Filtering Iterator

[Kevin Martin <kev82@...>]

Hi,

I need an iterator wrapper/decorator I can use with for that allows me to skip values that don't match a specified predicate. I've done a bit of searching, but haven't been able to find one. I've written the below code and it works for the simple example given, but I'm struggling to convince myself it's correct. Can anyone see anything wrong with it, or does it look ok?

Thanks,
Kevin

----------------------------------------------

function iterfilter(filter, iter, state1, var1)
	return function(state2, var2)
		while true do
			local t = table.pack(iter(state2, var2))
			if t[1] == nil then return nil end
			if filter(table.unpack(t)) then
				return table.unpack(t)
			end
			var2 = t[1]
		end
	end,
	 state1, var1
end

local t = {}
for k=1,100 do
	t[k] = tostring(k)
end

local function div3(x)
	return x % 3 == 0
end

local function div5(x)
	return x % 5 == 0
end

for _,v in iterfilter(div3, iterfilter(div5, pairs(t))) do
	print(v)
end