Merge sort demo with Racket because DrRacket debug mode shows the stack nicely

merge-sort-demo.rkt

#lang racket

(define (merge-sort l)
  (cond
    [(null? (cdr l)) l]
    [else (let-values
              ([(l1 l2) (split-in-half l)])
            (merge (merge-sort l1) (merge-sort l2)))]))

(define (split-in-half l)
  (split-at l (quotient (length l) 2)))

(define (merge l1 l2)
  (cond
    [(null? l1) l2]
    [(null? l2) l1]
    [(<= (car l1) (car l2))
     (cons (car l1) (merge (cdr l1) l2))]
    [(<  (car l2) (car l1))
     (cons (car l2) (merge l1 (cdr l2)))]))

(merge-sort '(45 3 2 5 80 38 44 92 3 6 -3 -7 9 0 4 85))