• Continue partners!
• Lab and reading in the back of the room. I don't know why the reading printed so small.

Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Representing images.
• Thinking about drawings through composition/decomposition.
• The underlying representation.
• Pure approaches vs impure approaches.

Preliminaries

Admin

• Review sessions:
  • Wednesday, 8pm (Zachary)
  • Thursday, 10am (Sam)
  • Thursday, 8pm (Caleb)
• I don't know why it's so hard to print from DrRacket. I'm looking into the issue.
• I hear that some of you are starting to get the "cs rush" - the joy of realizing that you've solved a hard problem.

Upcoming Work

• Reading for Wednesday Homogeneous Lists
• Exam 1
  • Electronic due TONIGHT: http://bit.ly/151-2015F-exam1
  • Printed version due TOMORROW: Keep cover sheet separate
  • Epilogue due TOMORROW NIGHThttp://bit.ly/151-2015F-exam1epi
• Today's Lab writeup (due before class Friday)
  • Email to grader-151-01@cs.grinnell.edu
  • Subject: CSC 151 Lab Writeup Class 15 (Your Names)
  • Exercise:

Extra Credit Opportunities

Academic

• Any visit to the current show in the Faulconer gallery
• No CS Table this week - It's advising week!
• Wednesday CS Extra this week, 4:15 in 3821: Ursula Woltz on Building Coding Communities
• Thursday CS Extra this Week, 4:15 in 3821: SamR on The Architecture of Mediascript

Peer Support

• Pals of PALS, pals@grinnell.edu, normally Saturday at 7:45 am (breakfast included), Sunday at 4:45, and Mondays at 4:45. Requires sign up in advance. Fundraising activity Saturday at 10:30 at 824 High Street.
• Pun Club, Saturdays, 4pm, Way over Younker.
• Singers concert on Family weekend! Sept. 26, 2pm., Sebring-Lewis
• Orchestra concert on Family weekend! Sept. 26, 2pm., Sebring-Lewis

Non Extra-Credit Activities

• EE's show in Smith
• Grinnell Homecoming Parade Thursday at 5:30 p.m. - Small town homecoming is an interesting experience that everyone should see once

Questions

When I run my procedure, instead of seeing a result, I see something like <procedure:hop.sadasfasffsdad#1231321>

(define my-proc
  (lambda (a b c)
    (o (section max a <>) (section max b <>) (section max c <>))))
> (my-proc 1 2 3)
#<procedure:...gigls/higher.rkt:215:4>

This means that you've written a procedure that returns a procedure. Congratulations! Many (non-Grinnell) CS majors don't learn how to do this until their senior year. But that's probably not what you wanted. Send me your code and I'll help you figure it out.

How many tests should we have in problem 4?

Enough that you are confident that a procedure written by any well-intentioned but incompetent programmer that passes your tests will always be correct. Probably about eight or so different cases in which you look at the minutes and seconds of each.
* EG says: Don't only write similar tests like "1 min 3 sec plus 2 min 3 sec" "2 min 3 sec plus 3 min 4 sec".)

Should we try times that go over an hour?

Yes, that would be good. But they will give large numbers of minutes; you should not worry about dealing with hours.

I got `Contract violation! Expect a lawyer to appear soon. Expected number?. Got procedure!

(+ + -) will give you that error, as will any attempt to use a procedure when Scheme expects a number.

Do you need a picture for the last problem?

No. The kitten has suffered enough.

Representing images

Thinking about drawings through composition/decomposition

The underlying representation

Pure approaches vs impure approaches