Tiny JSON parser in Lua.

tjson.lua

-- JSON parser originally from qjson.lua
local function decode(json --[[@param json string]]) ---@return table
	local ptr = 0
	local function consume(pattern --[[@param pattern string]]) ---@return string?
		local start = json:find("^%S", ptr)
		if start then ptr = start end

		local start, finish, match = json:find(pattern, ptr)
		if start then
			ptr = finish + 1
			return match or true
		end
	end

	local object, array
	local function number() return tonumber(consume("^(%-?%d+%.%d+)") or consume("^(%-?%d+)")) end
	local function bool() return consume("^(true)") or consume("^(false)") end
	local function string() return consume("^\"([^\"]*)\"") end
	local function value() return object() or string() or number() or bool() or array() end

	function object()
		if consume("^{") then
			local fields = {}

			while true do
				if consume("^}") then return fields end
				local key = assert(string(), "Expected field for table")
				assert(consume("^:"))
				fields[key] = assert(value(), "Expected value for field " .. key)
				consume("^,")
			end
		end
	end

	function array()
		if consume("^%[") then
			local values = {}
			while true do
				if consume("^%]") then return values end
				values[#values + 1] = assert(value(), "Expected value for field #" .. #values + 1)
				consume("^,")
			end
		end
	end

	return object() or array()
end