ML reference type and mutable data

(* checking if two lists are equal *)
let rec list_equals  = function
    ([],[]) -> true
  |([],_) -> false
  |(_,[]) -> false
  |(x::xs,y::ys) -> if x = y then list_equals (xs, ys) else false;;

list_equals ([],[]);;

list_equals ([7], []);;

list_equals ([7;2], [7]);;

list_equals ([7;2], [7;2]);;

(* Pattern matching cannot check for equality of variables *)
(* THIS IS NOT GOING TO WORK: *)
let rec list_equals  = function
    ([],[]) -> true
  |([],_) -> false
  |(_,[]) -> false
  |(x::xs,x::ys) -> list_equals (xs, ys)
  | _ -> false;;

CSci 4651 course.