how can i append a value to a tuple inside a list in Haskell? : For example, if I have a list of tuples such as [("a1", ["a2", "a3"]), ("b1", ["b2", "b3"])], and i want to add "a4" using "a1" "a4" as an input to update the list so that we get 
[("a1", ["a2", "a3", "a4"]), ("b1", ["b2", "b3"])] as an output, how would I go about approaching this? I know that we can't literally "update" a tuple, and that I have to make an entirely new list