• New Partners!

Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Quiz.
• Lab.
• Debrief.

Preliminaries

Admin

• Grades distributed via email.
  
  • Yes, I take comments and corrections.
  • No, you can't now do the labs you missed.
  • As some of you have discovered, I didn't catch all absences, but I caught many, and absences do affect your grade.
  • I have promised a number of people that I will revisit their exam 2 grade at the end of the semester and see how much of an impact dropping it has had. I will do so for anyone who asks me during finals week.

Upcoming Work

• Lab writeup (paper!): Exercises 1 and 3
• Reading for Tuesday: Trees
• HW7 due Tuesday at 10:30.
• Exam 3 distributed Wednesday.

Extra Credit Opportunities

Academic

• Joe Palca talk Tuesday at 7:30 p.m. in Sebring-Lewis.
• Scholars Convocation Wednesday at noon: Alison Bechdel.
• CS Extras Thursday: ???
• CS Table Friday: ???

Peer Support (Afternoon Section)

• EE (and SGAVPAA and IT) talk Tuesday at noon in JRC 101.
• Wednesday at 4:30 in Noyce 1302. Psychology Alumni Job Talk Series, Alex 'um from ACT.
• How an admitted student this coming Sunday night! Contact JMU for info.
• Many things the following weeks.
• Womens Tennis Sunday against Central.
• ISO Show, Saturday night 7-9 pm at Harris. Many live performances.

Miscellaneous

Nothing at present

Other Good Things (no extra credit)

• Student research seminar this week.

Questions

Quiz

Lab

• Each call to cons creates one pair.
• Each null is a slash within the corresponding element of the pair
• Each non-null value should have an arrow pointing to it

Debrief

Why do we do this?

• Because I told you to?
• To understand the underlying representation of lists and other structures that we sometimes creates.
  • We will be creating more complex structures starting tomorrow.
  • We can finally understand why we get the period for non-lists.
  • In some cases, we can see why lists behave the way they do.

Printing a pair

 Print an open paren
 Print the car
 Loop over the cdr
   cdr is null: print right paren
   cdr is a pair: print the car and do it again with the cdr
   cdr is not a pair: print a period and the cdr and a right paren

Checking listness / writing listp?

• A list is either null or a pair of anything and a list.
• So
  • Check if the parameter is null
    • Yes -> Done
  • Check if the parameter is a pair
    • No -> Done
    • Yes -> Check if the cdr is a list. How? Magic recursion fairy