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

function render(element)
	if type(element) == "string" then
		-- TODO: escape
		return element
	end
	if element[1] then
		return join(map(element, render))
	end

	local close_tag = "</"..element.type..">"
	local self_closing = element.type == "meta"
	if self_closing then
		close_tag = ""
	end

	return "<"..element.type
		..join(map(element.things, function(value, key)
			if type(key) == "number" then return "" end
			-- TODO: escape
			return " "..key.."='"..value.."'"
		end))
		..">"
		..join(imap(element.things, render))
		..close_tag
end

local function basic_element(name)
	return function(things)
		return { type = name, things = things }
	end
end

function a(things)
	if not things.href then
		print("WARNING: Link `"..ijoin(things).."` doesn't have a href.")
	end
	return basic_element("a")(things)
end

head = basic_element("head")
body = basic_element("body")
title = basic_element("title")
h1 = basic_element("h1")
h2 = basic_element("h2")
h3 = basic_element("h3")
h4 = basic_element("h4")
h5 = basic_element("h5")
h6 = basic_element("h6")
ul = basic_element("ul")
ol = basic_element("ol")
li = basic_element("li")
p = basic_element("p")
meta = basic_element("meta")

local link = a{href = "https://nulo.in",
	"Hola, soy html.lua"}

local head_block = head{
	meta{charset = "utf-8"},
	title{"Hello world"},
}
local body_block = body{
	link,
}

print(render{head_block, body_block})