• New partners!

Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Lab.

Preliminaries

Admin

• Sending HW questions to SamR (and probably CC)
  • Don't forget to carbon copy your partner when you submit questions.
  • Don't forget to use topics like HELP NEEDED ON HW5! when you email me questions.
  • Don't forget to include code when you email me questions.
  • Resend the email if I don't answer within 24 hours.

Upcoming Work

• Reading for Tuesday: Heterogeneous Lists
• HW 5 due Wednesday
• Today's Lab writeup (due before class Wednesday)
  • Exercise: 3ef
• Exam 2 to be distributed tomorrow.

Extra Credit Opportunities

Academic

• CS Table Tuesday: Barbie and the "Internet of Things"
• CS Extras Thursday: Blake Creasey on Watson

Peer Support

Other Good Things

• Friends of Drake Library book sale this weekend.

HW Questions

Do you have hints on problem 1?

I'd probably write some helper functions.

How do I mix if and map?

    (map (lambda (x) (if (even? x) ....)) 
         (iota num))

Question 2 on the exam asks us to take a function as a parameter. Can we really do that?

Yes. You've seen it happen in other cases, such as with map or ls. Here's a simple example.

    ;;; Procedure:
    ;;;   apply-to-two
    ;;; Parameters:
    ;;;   fun, a one-parameter function 
    ;;; Purpose:
    ;;;   Apply fun to the value 2
    ;;; Produces:
    ;;;   val, a value
    ;;; Preconditions:
    ;;;   fun must accept an integer as an input
    ;;; Postconditions:
    ;;;   val = (fun 2)
    (define apply-to-two
      (lambda (fun)
        (fun 2)))

    > (apply-to-two square)
    4
    > (apply-to-two increment)
    3
    > (apply-to-two (lambda (x) (+ 7 (* x 2))))
    11

One of the functions is wrong on problem 2, isn't it?

Yes. Sorry.

How can I recolor the dots?

    ;;; Procedure:
    ;;;   recolor-dot
    ;;; Parameters:
    ;;;   dot, a drawing
    ;;; Purpose:
    ;;;   Recolor dot to match the requirements from problem
    ;;;   2 of assignment 5 of section 2 of CSC 151 2015F
    ;;; Produces:
    ;;;   recolored-dot, a drawing
    ;;; Preconditions:
    ;;;   [None]
    ;;; Postconditions:
    ;;;   (drawing-color recolored-dot) = "blue" if the y position of
    ;;;     of dot < 50
    ;;;   (drawing-color recolored-dot) = "red" otherwise
    ;;;   (drawing-left recolored-dot) = (drawing-left dot)
    ;;;   (drawing-top recolored-dot) = (drawing-top dot)
    ;;;   (drawing-width recolored-dot) = (drawing-width dot)
    ;;;   (drawing-height recolored-dot) = (drawing-height dot)

    ...

    (map recolor-dot (....))

How would you handle the recoloring of the dots in problem 2?

I'd write a separate helper function

    ;;; Procedure:
    ;;;   recolor-point
    ;;; Parameters:
    ;;;   point, a drawing
    ;;; Purpose:
    ;;;   Recolor point based on its position
    ;;; Produces:
    ;;;   colored-point, a drawing
    ;;; Preconditions:
    ;;;   [No additional]
    ;;; Postconditions:
    ;;;   If y < 50, colored-point is blue
    ;;;   Otherwise, colored-point is red

How do we compute a random number in problem 3?

(random n) gives an integer between 0 and n-1, inclusive.

Lab

Pretend Purple is (irgb 255 0 255)

Section 1 wants you to know that your answer to 3a will look something like

(define horiz-black-to-blue 
  (lambda (width height)
    (image-compute
     (lambda (col row)
       ...)
     width height)))

Writeup 3ef