• New partners!

Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Quick Comments from Sam.
• Lab.
• Possible Debriefing.

Preliminaries

Admin

• We've seen more DrRacket crashes this semester than in the past few years combined. And we're not sure why.
  • Save regularly!
  • Save a backup!

Upcoming Work

• Assignment 3.
  • Due TONIGHT at 10:30 p.m.
  • Don't forget the prologue and epilogue!
• Exam 1 to be distributed tomorrow
• Lab writeup for lab 9 (today), exercise 3a: http://bit.ly/151-2015S-lab09
• Readings for Wednesday:
  • Testing Your Procedures

Extra Credit Opportunities

Academic

• Wednesday, February 4, 12:00 noon, JRC 101, Scholars' Convication: "The Fight for Economic Justice from the Streets of Chicago" by Virginia Parks.
• Any other event in this Rosenfield symposium.
• Thursday extra this week.
• Friday, February 6, 12:00 noon, Science 3821, CS Table, Summer Research Opportunities for CS Students
• TEDx Grinnell, sometime in February.

Peer Support (Afternoon Section)

• Track and Field, Saturday at 10 a.m., the Bear Fieldhouse
• Men's Basketball, Saturday at 3:00 p.m., New Darby
• Swimming, Conference Championships, February 13-15, The Osgood

Recommended Events (no EC unless mentioned above)

• #OneGrinnell, Wednesday, February 4 at 4:15 p.m.

Questions

What do you do when DrRacket corrupts our files?

I deal with it on a case-by-case basis.

If we give advance notice of our birthday, can we have a party in class?

I will bring snacks and we'll sing a song, but that's about it.

How do we get the square inside the circle?

Two approaches.

Draw the square and the circle centered at (0,0). Circle has diameter size. Square has diameter (/ size (sqrt 2)). Shift to the correct position.

Draw a square of the correct size using square-thing. It can be anywhere. Draw the correct circular hole using circle-thing. Use center-peg to move the square.

Quick Overview

• Official topic from yesterday: Documentation
• Really important concept from yesterday: Think about procedures as taking input values, returning new values, and not changing their inputs.
• We break that concept today. We will look at procedures that change their parameters or the world around them.
• Two competing models of computation.
• Meta-thinking: Which works better, and in which circumstance.

Lab

• Reminder: 3a writeup

Debrief?

• DrRacket and GIMP both refer to images by numbers.
• If you close all of the windows associated with an image, GIMP forgets about it, and you get weird error messages.
• DrRacket is even more careful about things than Sam when making a sandwich. Subtle differences lead to huge errors. E.g., (image-save 23 "/home/rebelsky/desktop/modified.jpg")