SICP 学习1 -- 个人学习过程中的代码。有对有错。不做解释。

Welcome to DrRacket, version 5.1.1 [3m].

Language: R5RS; memory limit: 128 MB.

> 9defune (abs x)

. . reference to undefined identifier: 9defune

. . reference to undefined identifier: x

> (defune (abs x)

    (cond ((> x 0) x)

          ((= x 0) 0)

          ((< x 0) (- x)))) 

. . reference to undefined identifier: defune

> (define (abs x)

    (cond ((> x 0) x)

          ((= x 0) 0)

          ((< x 0) (- x)))) 

define-values: cannot change constant variable: abs

> (define (_abs x)

    (cond ((> x 0) x)

          ((= x 0) 0)

          ((< x 0) (- x)))) 

> (-abs 1)

. . reference to undefined identifier: -abs

> (_abs 1)

1

> (_abs -11)

11

> (_abs 0)

0

> (define (__abs x)

    (cond ((< x 0) -x)

          (else x)))

> (__abs -4)

. . reference to undefined identifier: -x

> (define (__abs x)

    (cond ((< x 0) (- x))

          (else x)))

> (__abs -4)

4

> (__abs 24)

24

> (__abs 0)

0

> (__abs -0)

0

> (define (___abs x)

    (if (< x 0)

        (- x)

        x))

> (___abs -5)

5

> (___abs 95)

95

> (___abs 0)

0

> (___abs -0)

0

> (else)

. else: not allowed as an expression in: (else)

> (else 4)

. else: not allowed as an expression in: (else 4)

> (and  1 3 4)

4

> (and  1 0 4)

4

> (and  1 #f 4)

#f

> (and  #t #f 4)

#f

> (and  1 #t 4)

4

> (or  1 #t 4)

1

> (or  #f #t 4)

#t

> (or  #f #f 4)

4

> (or  #f #f #f)

#f

> (not  #f)

#t

> (not  23)

#f

> (not  2)

#f

> (and (> x 5) (< x 0)

       )

. . reference to undefined identifier: x

> (define (A x) (and (> x 5) (< x 0)))

> (A 3)

#f

> (A 7)

#f

> (define (A x) (and (> x 5) (< x 10)))

> (A 7)

#t

> 10

10

> (+ 5 3 4)

12

> (- 9 1)

8

> (/ 6 2)

3

> (+ (* 2 4) ( - 4 6))

6

> (define a 3)

> (define b (+ a 1))

> (+ a b (* a b))

19

> (= a b)

#f

> (if (and (> b a) ( < b (* a b)))

      b

      a)

4

> (cond ((= a 4) 6)

        ((= b 4) (+ 6 7 a))

        (else 25))

16

> (+ 2 ( if (> b a ) b a ))

     

6

> (* (cond (( < a b ) a )

           (( < a b ) b)

           (else 1))

     (+ a 1))

12

> (* (cond (( > a b ) a )

           (( < a b ) b)

           (else 1))

     (+ a 1))

16

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

-37/150

> ;练习1.3

(define (lx_1.3 a b c) (- (+ a b c) (cond ((< a b) (if (< a c) a c))

                                          ((< b c) b)

                                          (else c))))

> (lx_1.3 1 2 3)

5

> (lx_1.3 11 2 3)

14

> ;练习1.4

(define ( a-plus-abs-b a b)

  ((if(> b 0) + -) a b))

> (a-plus-abs-b 1 2)

3

> (a-plus-abs-b -1 2)

1

> (a-plus-abs-b -1 -2)

1

> (a-plus-abs-b 1 -2)

3

> 1

1

> (1)

. . procedure application: expected procedure, given: 1 (no arguments)

> (define (p) (p))

> (define (test x y)

    (if ( = x y) x y))]

. read: illegal use of close square bracket

> (define (test x y)

    (if ( = x y) x y))

> (test 0 (p))

. . user break

>