local type Stack = record
	contents: {any}
	top: number
	push: function(Stack, any)
	pop: function(Stack)
	new: function(Stack): Stack
end
function Stack:push(val: any)
	self.top = self.top + 1
	table.insert(self.contents,val)
end
function Stack:pop(): any
	self.top = self.top -1
	if self.top < 0 then
		error("Stack underflow")
	end
	return table.remove(self.contents)
end
local stack_mt = {__index = Stack}
function Stack:new(): Stack
	return setmetatable({contents = {}, top = 0} as Stack, stack_mt)
end


-- operations

return Stack