Using Standard ML language to solve the problem using RECURSIVE definitions.

6. Write a function longest string that takes a string list and returns the longest string in the list. If the list is empty, return " (i.e., empty string). In the case of a tie, return the string closest to the beginning of the list. longest_string (["abc", "hello", "car", "apple"] >"hello" longest string (I) 39 CC .(*) For this problem, your implementation is required to use the build-in size function