There are really no such thing as a "functioning alcoholic". If they are still able to function in any way they are not an alcoholic
This has not been my experience.
My AH has been gainfully employed his whole life, with only 2 different employers for the last 25 years. He is successful, occasionally lectures, and considered an expert in his field. He takes home his pay cheque, never goes to the bar on evenings or weekends, does his chores, is polite and generally considerate to me. He is "functioning".
He also must have a drink by around 6 p.m. every single day, earlier on weekends. The tremors start around noon. He has only not drank on a 2 week hospitalization in the last 20+ years (caused by trying to quit cold turkey, had seizures and a mini stroke). He is an alcoholic by anyone's definition. He used to drink in the mornings and all day, but now post hospitalization just in the evening.
Alcoholics come in all varieties.