Writing in a Paris cafe, an art form and way of life perfected by many writers and philosophers of 20th century, appear to be fitting less well into the modern times. Still, there are some places in Paris where a customer with a laptop is welcome. I bet, if you come with an antique typewriter, you will be greeted even warmer.
On this my trip to Paris, I made a little discovery: one can dring only finitely many café au lait‘s. But gunpowder tea is a real solution for a long working session, it can be consumed in unlimited quantities. Also, it provides excellent value for money: you order a pot and then ask the waiter to top it up with hot water. High quality green tea can be topped up up to 6 times without obvious loss in quality. France has a wonderful tea tradition; teas from Damman are widely available in cafes and bistros, and their gunpowder tea is excellent.