[Haskell-beginners] Application of lookup function

Hi all. I'd like to apply lookup function (Data.Map) for what I am working on. Here is my code. data Person = Person {personId :: Int, name = String} data People = [Person] data State = InMembership | NoMemebership person1 = Person {1 = personId, "James" = name} person2 = Person {2 = personId, "Tom" = name} members = People [person1, person2] class Belonging a where belonging :: a -> [a] -> Bool -> State here is the problem... I don't know how to get to know whether a person is belong to members. I'd like to find it through a person's name. Can you suggest any examples?? Sincerely, Jeon