For 1.4

Review of basic for concepts, introduction to for/fold.

The review section contains a mix of “sequence-making” commands like in-range and lists. When the question gives a sequence-making command, write the list it will produce. When the question gives a list, write a sequence-making command that could be used to produce it.

To write list answers, give the first three items, then ... to the last item. The long list:

(list 21 22 23 24 25 26 27 28 29 30)

should be written:

(list 21 22 23 ... 30)

Short Answer Review

  1. (list 0 1 2 3 ... 19)

  2. (in-range 40)

  3. (in-range 0 9)

  4. (list 5 6 7 8 9 10 11)

  5. (in-range 19 29)

  6. (list 0 2 4 6 8)

  7. (list 10 200 30)

  8. Given the list XC, create a list of radius 20 solid circles with those colors.

     (define XC (list "red" "blue" "orange" "purple"))

  9. (list 100 99 98 ... 1)

Complete For Loops

  1. Make this list:
(list "100 bottles of beer on the wall"
      "99 bottles of beer on the wall"
      "98 bottles of beer on the wall"
      ...
      "1 bottles of beer on the wall"
      )

  1. Make a list of all of the odd numbers 1 through 101 that are not divisible by 7. The omitted numbers are marked #;NO-. Do not generate anything for your missing numbers.

    (list 1 3 5 #;NO-7 9 11 13 15 17 19 #;NO-21 23 ... 99 101)

Newer Material: in-naturals

Understanding in-naturals and two variable for-loops makes these a lot easier.

  1. Starting with the list XC from above, produce the list:

    (list (triangle 125 "solid" "red")
      (triangle 150 "solid" "blue")
      (triangle 175 "solid" "orange")
      (triangle 200 "solid" "purple"))

Now complete the For Exercises 1.5.

Newer Material: for/fold

The original review included two examples of for/fold.

Folding: Adding

You have 3 dollars. On your way to school, you find a quarter, a dime, another dime, and 7 pennies. How much do you have?

(define FOUND (list 0.25 0.10 0.10 0.01 0.01 0.01 0.01 0.01 0.01 0.01))
(for/fold ([money 3.00])
          ([coin (in-list FOUND)])
  (+ money coin))

Folding: Drawing

You need a circle at each location in list.

(define C (circle 20 "outline" "black"))
(define PTS (list (make-posn 100 40) (make-posn 110 20) (make-posn 180 50)))
(for/fold ([pic (empty-scene 200 100)])
          ([p (in-list PTS)])
  (place-image C (posn-x p) (posn-y p) pic))

Note on Length

This material can be covered in a 90 minute class.