Scheme procedures, which sum up numbers, for demonstrating the difference between functional and imperative paradigm

functionalSum.scm

; calculating the sum of all numbers between start and end (including start and end)
(define functionalSum
  (lambda (start end)
    (if (= end start)
        end
        (+ end
           (functionalSum
            start
            (- end 1))))))

imperativeSum.scm

; calculating the sum of all numbers between start and end (including start and end)
(define imperativeSum
  (lambda (start end)
    (begin
      (define sum 0)
      (while
       (<= start end)
       (begin
         (set! sum
               (+ sum start))
         (set! start
               (+ start 1))))
      sum)))