smlj languge

2. (5 points) Write a function duplist of type 'a list -> 'a list whose output list is the same as the input list but with each element of the input list repeated twice in a row. For example, if the input is [1, 2, 3], the output list should produce (1, 1, 2, 2, 3, 3). If the input list 1. the output list should be []. o Note: Do not use explicit recursion but use one of the fold functions in order to get full credit. Do not write any additional functions, duplist should be the only function