SICP练习

1.2.lisp

(/ (+ 5 4 (- 2 (- 3 (+ 6 (/ 4 5)))) (* 3 (- 6 2) (- 2 7))))

1.3.lisp

(define (sum-of-two x y z) (if (> x y)
(if (> y z)
(+ x y)
(+ x z))
(if (> x z)
(+ x y)
(+ z y)))
)

1.5.lisp

(define (p) (p))
(define (test x y)
    (if (= x 0)
        0
        y))

(test 0 (p))

如果是正则序则直接进行参数替换，Ben会看到0;
如果是应用序则会先求参数的值，Ben会看到屏幕卡死(死循环)。

1.7.1.lisp

(define (abs x)
    (if (> x 0)
        x
        (- x)))

(define (average x y)
    (/ (+ x y) 2))

(define (improve guess x)
    (average guess (/ x guess)))

(define (good-enough? guess x)
    (< (abs (- (square guess) x)) 0.001))

(define (sqrt-iter guess x)
    (if (good-enough? guess x)
        guess
        (sqrt-iter (improve guess x)
                    x)))

(define (sqrt x)
    (sqrt-iter 1.0 x))

(sqrt 0.00002)

1.7.2.lisp

(define (abs x)
    (if (> x 0)
        x
        (- x)))

(define (average x y)
    (/ (+ x y) 2))

(define (improve guess x)
    (average guess (/ x guess)))

(define (good-enough? guess x)
    (< (abs (- (square guess) x)) 0.001))

(define (sqrt-iter guess x)
    (if (good-enough? guess x)
        guess
        (sqrt-iter (improve guess x)
                    x)))

(define (sqrt x)
    (sqrt-iter 1.0 x))

(sqrt 9999999999999999999999999)

1.7.3.lisp

(define (abs x)
    (if (> x 0)
        x
        (- x)))

(define (average x y)
    (/ (+ x y) 2))

(define (improve guess x)
    (average guess (/ x guess)))

(define (good-enough? guess x)
    (< (/ (abs (- (square guess) x)) guess)  0.000001))

(define (sqrt-iter guess x)
    (if (good-enough? guess x)
        guess
        (sqrt-iter (improve guess x)
                    x)))

(define (sqrt x)
    (sqrt-iter 1.0 x))

(sqrt 9999999999999999999999999)