Lab Quiz Solutions, Foundations of Computing, Week 4 -- Oct 17, 2000

Given these definitions:

(define x 1)

(define (add-x y)
  (+ x y))

(define (dbl-x x)
  (+ x x))

(define (add-sum y)
  (let ((sum (add-x x)))
    (+ sum y)))

(define (add-list y)
  (every add-x y))

For each of the following expressions, if the expression can be evaluated, write its value. If the expression cannot be evaluated, explain why not.

1. 1
1
   
   
2. x
1
   
   
3. 'x
x
   
   
4. y
   Can't evaluate, not defined
   
   
5. 'y
y
   
   
6. (x)
   Can't evaluate, 1 is not a procedure
   
   
7. '(x)
(x)
   
   
8. ('x)
   Can't evaluate, x is not a procedure
   
   
9. (add-x 1)
2
   
   
10. (add-x x)
2
    
    
11. (add-x 'x)
    Can't evaluate, x is not a number
    
    
12. (dbl-x 1)
2
    
    
13. (dbl-x x)
2 -- Here x is global, bound to 1
    
    
14. (dbl-x 2)
4 -- Here 2 is bound to the local x
    
    
15. (add-sum 1)
3
    
    
16. (add-list (1 2 3))
    Can't evaluate, 1 is not a procedure
    
    
17. (add-list '(1 2 3))
(2 3 4)
    
    
18. (add-x '(1 2 3))
    Can't evaluate, (1 2 3) is not a number
    
    
19. (keep even? (add-list '(1 2 3)))
(2 4)