ITEC 380 2012fall ibarland tlewis32

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hw10
Finishing N6
static scope

Due Dec.07 (Fri) at the start of class.
Submit: a hardcopy with the first question's fill-in-the-blanks¹ and the additional tests for N6 (since N4), and the additional/changed function(s) for N6 (since N4).
Since N6 is an extension N5, you don't need any code or test-cases for N5 different from N6.

We continue to build on the language implementation started in hw07. You can implement this homework in either Java or Racket. Please indicate in your submitted file, what sections of code are udpated and what is unchanged from hw09/hw09-soln. You don't need to turn in any hardcopy of unchanged-code (but submit a fully-working copy in the drop-box).

1. (Scope, 15pts) The racket form set! changes the binding of a variable:

   (define x 5) (set! x (* 2 x)) ; the variable x is now bound to 10.

   1. (define a 10) 2. (define b 20) 3. (define make-foo 4. (let {[b 30]} 5. (lambda () ; ← make-foo is bound to this function. 6. (let {[c 40]} 7. (lambda (cmd) ; ← make-foo returns this function as its answer. 8. (let {[d 50]} 9. (cond [(symbol=? cmd 'incA) (set! a (+ a 1))] 10. [(symbol=? cmd 'incB) (set! b (+ b 1))] 11. [(symbol=? cmd 'incC) (set! c (+ c 1))] 12. [(symbol=? cmd 'incD) (set! d (+ d 1))] 13. [(symbol=? cmd 'get-all) (list a b c d)])))))))

   1. 
      The scope of the a declared in line 1 is lines                  through                 .
   2. 
      The scope of the b declared in line 2 is lines                  through                 .
   3. 
      The scope of the b declared in line 4 is lines                  through                 .
   4. 
      The scope of the c declared in line 6 is lines                  through                 .
   5. 
      The scope of the d declared in line 8 is lines                  through                 .
   Suppose that make-foo is called exactly three times (but that a function returned by make-foo is not called).
   5. 
      How many variables named a are created?                 
   6. 
      How many variables named b are created?                 
   7. 
      How many variables named c are created?                 
   8. 
      How many variables named d are created?                 
   (Hint: Each of the above four answers are different.)

   (set! a 500) (set! b 600) (define counter1 (make-foo)) (define counter2 (make-foo)) (define counter3 (make-foo)) (counter1 'get-all) ; >>> TODO: (list                            ) (counter1 'incA) (counter1 'incB) (counter1 'incC) (counter1 'incD) (counter1 'get-all) ; >>> TODO: (list                            ) (counter2 'get-all) ; >>> TODO: (list                            )

2. (20pts) Complete N5, as per hw07—Interpreting N: project.

3. (15pts, including 5pts for implementing recursion)
   Complete N6, as per hw07—Interpreting N: project.

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©2012, Ian Barland, Radford University Last modified 2012.Dec.02 (Sun)

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