6.090 IAP '05 - Lecture 1 Solutions

Problem 1

4

5.5

42.

3

;The object 7 is not applicable.

-15

unspec

unspec

unspec

5

unspec

unspec

3

#t

;The object #t, passed as the first argument to integer-equal?, is not the correct type.

;The object 11 is not applicable

;Value: #[compiled-procedure 9 ("arith" #x44) #xF #xE1F5C3]

1

#t

10

128

Problem 2:

3

Problem 3:

(if #t (- (* 3 4) (/ 81 9)) 4)

Problem 4:

Numerous answers possible, here's a set:

(define x 4)
(define y 3)
(+ x (* y 3)))

(define q #t)
(define r #f)
(if q (if r 3 4) 7))

(define z 3)
(define a 1)
(+ 7 (if z (+ a z) 3)))

(define yum -1)
(= yum (* -1 (+ yum 2))))

(define thirty-four 102)
(define seventy-seven 1)
(< (if (not thirty-four) 34 thirty-four)
   (+ thirty-four (* seventy-seven (if seventy-seven -1 1))))

Problem 5:

1) abs - absolute value
(abs 5)
;Value: 5
(abs -5)
;Value: 5

(+ 3 (abs -2))

2) expt x y - exponentiation x^y
   sqrt x   - square root of x
(expt 12 2)
;Value: 144
(sqrt 9)
;Value: 3
2^4 = 16, so fill the blank with number >= 4

(if (> (expt 2 12) 15)
    (sqrt 2)
    (sqrt 4))

4) string-append - glue two (or more) string together
(string-append "yay" "rah")
;Value: "yayrah"

(string-apend "foo" "bar" "baz")

5) string-suffix? suffix s - does string s end with suffix
   string-search-forward pattern s - returns index of first occurance of
      pattern in string s.
s must be a string which ends in yowzah, which has "ow" at index 7

(define s "yayrahyowzah")
(if (string-suffix? "yowzah" s)
    (+ 7 (string-search-forward "ow" s))
    #f)