Trains and composted tickets

Home on a TGV (train à grande vitesse) - very fast non-stop train from Bordeaux to Paris. We remembered to composter our tickets as we entered the platform. Composter means to validate, and rather than having ticket inspectors at the barriers to the platforms, French (& Italians too) require you to compost your ticket at a yellow machine that stamps the time and date on it. If an inspector gets on the train and you haven't composté, you're in trouble. In Italy, you have to pay the total cost again. I don't know what they do in France, but don't want to find out.