generic.lua

local function map(f, iter, state, k)
	return function(state, k)
		local v
		k, v = iter(state, k)
		if k then
			return k, f(v)
		end
	end, state, k
end

local function identity(x) return x end

local tbl = {}

for i = 1, 10^6 do
	tbl[#tbl + 1] = i
end

for k, v in map(identity, ipairs(tbl)) do
	-- nothing
end

specific.lua

local ipairs = ipairs

local function ipairs_map(tbl, mapfunction)
	local iter, state, k = ipairs(tbl)
	return function(state, k)
		local v
		k,v = iter(state, k)
		if k == nil then return nil end
		return k,mapfunction(v)
	end, state, k
end

local function identity(x) return x end

local tbl = {}

for i = 1, 10^6 do
	tbl[#tbl + 1] = i
end

for k, v in ipairs_map(tbl, identity) do
	-- nothing
end