Make three test cases for this code (define (value-of-ds expr env) (cond ((number? expr) expr) ((eq? expr 'empty) '()) ((eq? (car expr) 'if-null) (let ((condition (value-of-ds (cadr expr) env))) (if ( What is the primary purpose of the provided code snippet?

a) Evaluating arithmetic expressions
b) Handling empty lists
c) Implementing conditional statements
d) Checking for null values