CS61A Summer 2011 Lab 4
1. Try these in Scheme:
(define x (cons 4 5) )
(define y (cons ’hello ’goodbye) )
(define z (cons x y) )
(car (cdr z) ) (cdr (cdr z) )
2. Predict the result of each of these before you try it:
(cdr (car z) )
(car (cons 8 3) )
3. Enter these definitions into Scheme:
(define (make-rational num den)
(cons num den) )
(define (numerator rat)
(car rat) )
(define (denominator rat)
(cdr rat) )
(define (*rat a b)
(make-rational (* (numerator a) (numerator b) )
(* (denominator a) (denominator b) ) ) )
(define (print-rat rat)
(word (numerator rat) ’/ (denominator rat) ) )
4. Try this:
(print-rat (make-rational 2 3) )
(print-rat (*rat (make-rational 2 3) (make-rational 1 4) ) )
5. Define a procedure +rat to add two rational numbers, in the same style as *rat above.
6. Now do exercises 2.2, 2.3, and 2.4 from SICP.
7. This week you’ll learn that sentences are a special case of lists, which are built out of pairs. Explore how that’s done with experiments such as these:
(define x ’(a (b c) d) )
(car (cdr x) )
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Lab 4 continued...
8. SICP ex. 2.18; this should take some thought, and you should make sure you get it right, but don’t get stuck on it for the whole hour. Note: Your solution should reverse lists, not sentences! That is, you should be using cons, car, and cdr, not first, sentence, etc.