local function map(list, func)
	local new_list = {}
	for key, value in pairs(list) do
		new_list[key] = func(key, value)
	end
	return new_list
end
local function join(list)
	local string = ""
	for key, value in pairs(list) do
		string = string .. value
	end
	return string
end

local function basic_element(name)
	return function(params, children)
		return "<"..name
			..join(map(params, function(key, value)
				return " "..key.."='"..value.."'"
			end))
			..">"
			..join(children)
			.."</"..name..">"
	end
end

local function a(params, children)
	if not params.href then
		print("WARNING: Link `"..join(children).."` doesn't have a href.")
	end
	return basic_element("a")(params, children)
end
print(a({ href = "https://nulo.in" }, {"Hola, soy html.lua"}))