The syntax for a do loop in Scheme is as follows: (do (( ) ...) ( ...) ...) For example, the following code determines the length of a list iteratively: (define (length lst) (do ((len O (+ len 1))) ((null? lst) len) (set! lst (cdr lst)))) Here is another example that sums the numbers between 1 and n iteratively: (define (sum n) (do (i 1 (+ i 1)) (sum 0)) ((> i n) sum) (set! sum (+ sum i))) ) Write an iterative function for sum-of-squares