The following recipe is how Root Beer Floats were made in 1919 (but not with fat free and diet ingredients, obviously!) at the first A&W Root Beer stand in Lodi, California.
Classic Summer Treat: Coat the inside of the glass with a smear of vanilla ice cream all around. Drop in a whole, heaping scoop of fat free ice cream. Top it off with A&W Diet Root Beer right to the rim of the glass.