Answer the following questions in SML$.$ Do not raise exceptions or include edge cases$/$empty list cases in the functions. In your answer to a question, you may reuse functions, types, classes, and methods that you have defined in the previous questions.

Here's what I have so far:

$1.$

datatype exp $=$

Const of int

$|$ Plus of exp $*$ exp

$|$ Pair of exp $*$ exp

$|$ Left of exp

$|$ Right of exp