• New Partners!

Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
  • Exam 2 returned.
• Lessons from yesterday's lab.
• A useful tool for repetition: for-each.
• Contrasting map, for-each, repeat, and recursion.
• Lab.
• Debrief.

Preliminaries

Admin

• Review sessions Thursday at 9:15am (Sam), 1:15pm (Sam), and 8pm (Alex).
• After reflecting, I flipped the topics for today's class and Friday's class. Sorry!
• My severe weather alert warning from KCCI is a "Fire Weather Warning". I'm not sure whether it has do do with the date or not.
• Three bad jokes. One out of three ain't bad.

Upcoming Work

• Lab writeup! Problems 8, 9, and 10. http://bit.ly/151-2015S-lab34
• Reading for Friday: Geometric Art
• Assignment 7 distributed: Producing Playful Polygons.

Extra Credit Opportunities

Academic

• CS Table Friday: Therac 25 (readings back of room or outside my office)

Peer Support (Afternoon Section)

• 7:30 p.m. on April 2: Gender as a Process. EE talks afterwards about using mathy things to understand gender.

Miscellaneous

• Tonight's "Moving Forward" discussion.
• Contact JMU to host a prospie. You also get a good dinner in quad and the ability to attend an incredible improv show. Sunday April 12th. Most importantly, you convince awesome people that they should come to Grinnell.

Questions

Exam 2 Returned

Strongest arguments:

• "The main goal of the exams is that we learn. We've learned. Exam grades are likely to be relatively consistent across exams, so not counting this exam is unlikely to have an effect on students who did not get inappropriate help."
• "Many of us worked very hard on this exam and should see rewards for our hard work."
• "You should have a policy that does not discourage people from coming forward."

Learning outcomes from yesterday's lab

• Select-all and Delete to clear an image.
• A few small tools and mechanisms for combining them give great opportunity.
• To use turtles successfully, you need to be able to determine where they are after each step (and, often, restore some characteristic).

A useful tool for repetition: for-each

• map apply a procedure to each value in a list and make a new list
• Sometimes we don't care about that new list. In cases like that, we use for-each.
• for-each is very useful for spirals.
  • See lab and reading for more details

Contrasting map, for-each, repeat, and recursion

> (map (lambda (x) (display x) (newline))
       (list "Happy" "April" "fool" "day"))
Happy
April
fool
day
'(#<void> #<void> #<void> #<void>)
> (for-each (lambda (x) (display x) (newline))
            (list "Happy" "April" "fool" "day"))
Happy
April
fool
day
> (repeat 4
          (lambda (x) (display x) (newline))
          (list "Happy" "April" "fool" "day"))
(Happy April fool day)
(Happy April fool day)
(Happy April fool day)
(Happy April fool day)
>

Lab/Debrief

• Moral 1: You can repeat a basic action to produce a more complex action (e.g., for-each with turn/move gives you a spiral). You can repeat a more complex aaction multiple times to produce something even more complex.
• Moral 2: Systematic complex procedures can produce systematic complex results.
• Moral 3: Systematic complex procedures can produce surprisingly unpredictable results.
• Moral 4: Serendipity
• Moral 2: You can repeat