modlib/luon.lua

local assert, next, pairs, pcall, error, type, table_insert, table_concat, string_format, string_match, setmetatable, select, setfenv, math_huge, loadfile, loadstring
	= assert, next, pairs, pcall, error, type, table.insert, table.concat, string.format, string.match, setmetatable, select, setfenv, math.huge, loadfile, loadstring

local count_objects = modlib.table.count_objects
local is_identifier = modlib.text.is_identifier

-- Build a table with the succeeding character from A-Z
local succ = {}
for char = ("A"):byte(), ("Z"):byte() - 1 do
	succ[string.char(char)] = string.char(char + 1)
end

local function quote(string)
	return string_format("%q", string)
end

local _ENV = {}
setfenv(1, _ENV)
local metatable = {__index = _ENV}
_ENV.metatable = metatable

function new(self)
	return setmetatable(self, metatable)
end

function aux_write(_self, _object)
	-- returns reader, arguments
	return
end

aux_read = {}

function write(self, value, write)
	local reference = {"A"}
	local function increment_reference(place)
		if not reference[place] then
			reference[place] = "B"
		elseif reference[place] == "Z" then
			reference[place] = "A"
			return increment_reference(place + 1)
		else
			reference[place] = succ[reference[place]]
		end
	end
	local references = {}
	local to_fill = {}
	-- TODO sort objects by count, give frequently referenced objects shorter references
	for object, count in pairs(count_objects(value)) do
		local type_ = type(object)
		if count >= 2 and (type_ ~= "string" or #reference + 2 < #object) then
			local ref = table_concat(reference)
			write(ref)
			write"="
			write(type_ == "table" and "{}" or quote(object))
			write";"
			references[object] = ref
			if type_ == "table" then
				to_fill[object] = ref
			end
			increment_reference(1)
		end
	end
	local function is_short_key(key)
		return not references[key] and type(key) == "string" and is_identifier(key)
	end
	local function dump(value)
		-- Primitive types
		if value == nil then
			return write"nil"
		end
		if value == true then
			return write"true"
		end
		if value == false then
			return write"false"
		end
		local type_ = type(value)
		if type_ == "number" then
			return write(string_format("%.17g", value))
		end
		-- Reference types: table and string
		local ref = references[value]
		if ref then
			-- Referenced
			return write(ref)
		elseif type_ == "string" then
			return write(quote(value))
		elseif type_ == "table" then
			local first = true
			write"{"
			local len = #value
			for i = 1, len do
				if not first then write";" end
				dump(value[i])
				first = false
			end
			for k, v in next, value do
				if type(k) ~= "number" or k % 1 ~= 0 or k < 1 or k > len then
					if not first then write";" end
					if is_short_key(k) then
						write(k)
					else
						write"["
						dump(k)
						write"]"
					end
					write"="
					dump(v)
					first = false
				end
			end
			write"}"
		else
			-- TODO move aux_write to start, to allow dealing with metatables etc.?
			(function(func, ...)
				-- functions are the only way to deal with varargs
				if not func then
					return error("unsupported type: " .. type_)
				end
				write(func)
				write"("
				local n = select("#", ...)
				local args = {...}
				for i = 1, n - 1 do
					dump(args[i])
					write","
				end
				if n > 0 then
					write(args[n])
				end
				write")"
			end)(self:aux_write(value))
		end
	end
	for table, ref in pairs(to_fill) do
		for k, v in pairs(table) do
			write(ref)
			if is_short_key(k) then
				write"."
				write(k)
			else
				write"["
				dump(k)
				write"]"
			end
			write"="
			dump(v)
			write";"
		end
	end
	write"return "
	dump(value)
end

function write_file(self, value, file)
	return self:write(value, function(text)
		file:write(text)
	end)
end

function write_string(self, value)
	local rope = {}
	self:write(value, function(text)
		table_insert(rope, text)
	end)
	return table_concat(rope)
end

function read(self, ...)
	local read = assert(...)
	-- math.huge is serialized to inf, 0/0 is serialized to -nan
	-- TODO verify this is actually the case, see https://en.wikipedia.org/wiki/Printf_format_string
	setfenv(read, setmetatable({inf = math_huge, nan = 0/0}, {__index = self.aux_read}))
	local success, value_or_err = pcall(read)
	if success then
		return value_or_err
	end
	return nil, value_or_err
end

function read_file(self, path)
	return self:read(loadfile(path))
end

function read_string(self, string)
	return self:read(loadstring(string))
end

return _ENV