Overview

• Preliminaries.
  • Upcoming work.
  • Admin.
  • Questions on HW6.
• Reflection.
• Questions.
• Lab.

Preliminaries

Upcoming Work

• Reading for Tuesday: Recursion with Helper Procedures
• Today's lab writeup: Exercises 4 and 5
  • CSC 151.02 Writeup 16: Recursion Basics
• HW6

Admin

• Kim will be teaching class Tuesday. Thanks Kim!
• Mr. Stone will be teaching class Wednesday and Friday.
• Exam 2 will be distributed on Wednesday.
• No quiz on Friday!
• Choose your own (new) partners tomorrow. Strive to find someone you have not worked with before.
• Extra credit for volunteers to do eboards on Tuesday, Wednesday, and Friday.
  • KS, Tuesday
  • CS, Friday
• Extra credit:
  • Convocation Wednesday, March 5.
  • Orchestra
    • With additional Narration and Animation, Wednesday, March 5
    • 7:30 p.m. in Sebring-Lewis
  • Grinnell image presentations at noon on Thursday and Friday.
  • First Years: How to Use Your Summer, 8-9 pm on March 6 in JRC 101.
  • Balancing Acts
    • Friday, 7 March at 7:30 in Flanagan
    • Saturday, 8 March at 7:30 in Flanagan
    • Sunday, 9 March at 2:00 in Flanagan
  • Neverland Players this weekend
    • Friday, 7 March at 7:00 in the Wall
    • Saturday, 8 March at 2:00 in the Wall
    • Saturday, 8 March at 7:00 in the Wall
    • Sunday, 9 March at 2:00 in the Wall
  • Men's Tennis, Saturday, 8 March (8 am or 4pm)

Questions on HW6

Should every procedure have documentation?

Yes. You can be casual on preconditions and postconditions

Will our notes suffice for 3 and 4?

Yes, provided I remember to tell the graders.

What should the inputs to problem 4 look like?

It's a program, so it doesn't really need inputs. Just show me the sequence of procedure calls to generate the image. E.g.,

    (define canvas (image-new 400 400))
    (render-polar-rose-on-image! canvas 50 23 "blue")

Reflection

What did you learn on Friday?

• Recursion
• Using a function within a function so as to achieve repetition
• Purpose: Achieve repetition
• Technique: Implement a procedure by making that procedure call itself (some of the time)
  • If the condition holds, call itself
  • If the condition does not hold, stop
  • Or vice versa
• If we're working with a list, we can throw away an element of the list each time and stop when there's nothing left in the list.
• Why not just use map?
  • Can't have the condition part; always deals with every element in the list
  • map only produces a list; sometimes we want to produce values other than a list.

• General form of a recursive procedure

  (define fun (lambda (vals) (if (TEST) (fun ) BASE-CASE)))

Questions

Lab