Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Sequencing operations in Scheme.
• The drawings-as-values model, revisited.
• Why define your own procedures?
• How to define your own procedures.
• Evaluating expressions in Scheme.

Preliminaries

Admin

• New partners! These will also be your homework partners.
• Office Hours: Normally: 10:00-11:00 MTWF
• Please follow the suggestions for the title of your email messages; many of the graders have filters running to automatically move work to grade into a particular folder.
• I'm going to try to talk less today; we'll see how well I do.
• Quiz 2 is Friday
  • Evaluation in Scheme (define, order of evaluation, etc.)
  • Drawings as values
  • Not procedures
• Don't forget: Review sessions Thursday at 9:00 a.m. and 1:15 p.m., Mentor session Thursday at 8:00 p.m.
• I'm going to try talking less at the start of class today. You'll need to take responsibility for reading the outline/eboard for announcements.
• We normally expect today's lab to take about 1.5 class periods.

Upcoming Work

• Assignment 3.
  • Due next Tuesday at 10:30 p.m.
• Lab writeup for lab 6 (today), due Friday before class: http://bit.ly/151-2015S-lab06
• No additional readings for Friday.

Extra Credit Opportunities

Academic

• Friday, 12:10 p.m., JRC 224A (Day PDR), CS Table, To be determined.

Peer Support (Afternoon Section)

• Swimming, Friday, January 30, 6:30 p.m., Osgood Natatorium
• Swimming, Saturday, January 31, noon, Osgood Natatorium
• Men's Tennis, Saturday, January 31, Field House

Recommended Events (no EC unless mentioned above)

• Gene Gaub Concert today!
• #OneGrinnell, Wednesday, February 4 at 4:15 p.m.

Questions

Notes from Lab

How Sam Writes Questions

"Write a procedure, (centered-circle side left top)", means

The procedure name is centered-circle

The parameters are side, left, and top

I should write

    (define centered-circle
      (lambda (side left top)
        ...))

Getting Started

Gimp, MediaScheme->DBus Server, Check for DrRacket 5.3.6 will become automatic

Vocabulary

You are learning a vocabulary. You have some responsibility to remember the words and the parameters. You should find the best way to do that for you. I recommend the index cards for reference.

Checking Your Answers

One experiment is not enough!

; inputs val, lower-bound, upper-bound
> (bound 5 0 10)
> (bound -5 0 10)
> (bound 15 0 10)
> (bound 5 10 0)

; inputs to centered-square: edge-length, center-x, center-y
> (image-show (drawing->image (centered-square 40 50 60) 100 100))
> (image-show (drawing->image (centered-square 20 40 30) 100 100))
> (drawing-width (centered-square 1000 20 30))
...
> (image-show (drawing->image (centered-square -20 40 30) 100 100))

Computer Programming as Video Game

Level 1: When I click "Run", it doesn't complain.

Level 2: When I enter an expression, it doesn't complain.

Level 3: When I enter an expression, it produces something close to the value that I expect.

Level 4: When I enter an expression, it produces something I know is correct.

Level 5: When I enter a large variety of expressions, it always produces the right thing.

Formatting Your Code

Sarah says "Hit enter so that it's clean and pretty."

Samh says "After hitting enter, use Ctrl-I

Save!

DrRacket will crash.

You will accidentally close the window.

Saving will make you happier, and should be automatic.