Welcome to DrScheme, version 204.
Language: Textual (MzScheme, includes R5RS).
> (map (compose floor log2) '(1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 
17 18 19 20))

(0
 1.0 1.0
 2.0 2.0 2.0 2.0
 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0
 4.0 4.0 4.0 4.0 4.0)

> (map (compose ceiling log2) '(1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 
17 18 19 20))

(0
 1.0  
 2.0 2.0
 3.0  3.0 3.0 3.0 
 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 
 5.0 5.0 5.0 5.0)

> (apply + (map (compose floor log2) '(1 2 3 4 5 6 7 8 9 10 11 12 13 
14 15 16 17 18 19 20)))
54.0
> ((compose floor log2) 1023)
9.0
> (apply + (map (compose ceiling log2) '(1 2 3 4 5 6 7 8 9 10 11 12 13 
14 15 16 17 18 19 20)))
69.0
> 

(define compose
  (lambda (f g)      ;; compose is a procedure

     (lambda (x)     ;;
        (f (g x))    ;;  whose arguments and value are procedures
   )))          

(define log2
  (lambda (n)
    (/ (log n) (log 2))))


Fill in the blanks: 

    > (define mystery
         (lambda (+ -)
           (+ (- x y) (- y x))))
    > (define x 10)
    > (define y  5)
    > (mystery * /)
    ?????

http://www.cns.uni.edu/~wallingf/teaching/154/sessions/session06.html