my-object🔗 i

> (require my-object)

> (define p(object [x1][y2]))

> p

(object [x 1] [y 2])

> (object? p)

#t

> (p'x);by the way, you can use #'x here instead of 'x

1

> (p'y)

2

> (define p2(p'x#:->3))

> p2

(object [x 3] [y 2])

> (define (posnx0y0)

(object [xx0][yy0]

[add(λ (p)(posn(+ x(p'x))(+ y(p'y))))]

[->list(λ ()(list xy))]))

> (define p3(send (posn12)add(posn34)))

> (send p3->list)

'(4 6)

> (define p3(posn12))

> (define p4(object-extend p3[x3]));or (p3 'x #:-> 3)

> (send p4->list)

'(3 2)

> (define (3d-posnx0y0z0)

(object-extend (posnx0y0)

#:inherit(xy)

[zz0]

[add(λ (p)(3d-posn(+ x(p'x))(+ y(p'y))(+ z(p'z))))]

[->list(λ ()(list xyz))]))

> (3d-posn123)

(object [x 1] [y 2] [add #<procedure>] [->list #<procedure>] [z 3])

> (require my-object)

> (define (make-fishsz)

(define sizesz);private mutable field

(object [get-size(λ ()size)]

[grow(λ (amt)

(set! size(+ amtsize)))]

[eat(λ (other-fish)

(grow(send other-fishget-size)))]))

> (define charlie(make-fish10))

> (send charlieget-size)

10

> (send charliegrow6)

> (send charlieget-size)

16

> (define (make-hungry-fishsz)

(object-extend (make-fishsz)

#:inherit(eat)

[eat-more(λ (fish1fish2)

(eatfish1)

(eatfish2))]))

> (send (make-hungry-fish32)get-size)

32

> (define (make-picky-fishsz)

(object-extend (make-fishsz)

#:super([super-growgrow])

[grow(λ (amt)

(super-grow(* 3/4amt)))]))

> (define daisy(make-picky-fish20))

> (send daisyeatcharlie)

> (send daisyget-size)

32