Quicksort in Scheme

(define (quicksort lst op)
 (if (null? lst)
 lst
 (let* ((one (car lst))
 (left (filter (lambda (x)
 (op x one))
 (cdr lst)))
 (right (filter (lambda (x)
 (not (op x one)))
 (cdr lst))))
 (append (quicksort left op) (list one) (quicksort right op)))))

(screen:clear-window (screen:make-window))

CL-USER 9 > (defun x (c)
              (let ((i 4))     ; defining/binding local variable i
                (loop while (< i 10) do
                      (print i)
                      (incf i))))
X

CL-USER 10 > (x :foobar)

4 
5 
6 
7 
8 
9 
NIL

(set-frame-font "Inconsolata 12" nil t)

sudo apt remove --purge emacs-bin-common emacs-el emacs-gtk