Northeastern CS 2500 Blog

Self-reproducing code

Today in class I gave 2500 students an outgoing challenge to take home for vacation: come up with a Scheme expression that evaluates to itself. For example, the expression

 (list 'cons '(+ 3 5) (list 'quote (list)))

evaluates to the list

 (cons (+ 3 5) '())

which, unfortunately, doesn't match the list

 (list 'cons '(+ 3 5) (list 'quote (list)))

so it doesn't qualify. (To get Dr.Scheme to print lists out like this, you'll have to go to "Choose Language" and change the "Output Style" option to "write.")

In other words, can you come up with an expression exp such that

 (equal? exp 'exp)

produces true? (Note that the very first program we wrote this semester, 8, is a possible solution, since numbers self-evaluate in Scheme. But that's too trivial an answer to be interesting.)

To solve this problem, you may find it useful to know that

 (quote anything)

is the same in Scheme as

 'anything

You can, for example, try comparing what happens if you evaluate the two expressions

 (quote (string-append (f (+ 3 2)) "foo")) '(string-append (f (+ 3 2)) "foo")

You might also bear in mind that a pair of square brackets, in Dr.Scheme, is completely interchangeable with a pair of parentheses—it's just a convention that we use square brackets for cond clauses and parentheses for function calls.

The self-evaluating-expression puzzle is just the Scheme variation of an old Computer Science problem: writing a program that, when executed, prints out exactly the original source text of the program. (You can try this in any other programming language you know, e.g. Java or C.) If either variation seems impossible, on the face of it, be assured that (1) it can be done, and (2) if you can figure out how to do it, you will achieve enlightenment.

Alternatively, since this is 2009, you can always use google or wikipedia and find a solution—then you'll understand how to do it, but will not be enlightened. That is, you won't actually deepen your understanding of the nature of programs and computation; alas, that's how these things work. (You won't have as much fun, either.)

One final comment, and one final question.

The comment:
Writing a program that prints itself (or a Scheme expression that evaluates to itself) might seem like a somewhat pointless thing to do. But it turns out that the ability to write such a program is the core idea behind one of the most elegant techniques ever devised for breaking into a computer, the so-called "Thompson hack." This technique was described by Ken Thompson (one of the inventors of the Unix operating system) in his Turing Award lecture, Reflections on trusting trust. Again, I recommend that you solve the puzzle before reading Thompson's lecture.
The question:
In the honors-track lectures, we discussed the idea of fixed points of functions. What does the idea of fixed-points have to do with this puzzle?

Good luck with your exams, and have a great vacation.

—Olin

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Final homeworks are up

Regular-track homework 10 and honors-track homework 9h are both posted.

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Test 2 details

The test will be held 6:30 PM–9:30 PM, in West Village F, room 20 this Monday (11/23), for students in all sections of the class.

The test will be open book: you can bring any kind of hardcopy you wish, including the textbook, notes, and printouts. You may not bring or use calculators, computers, cell phones, etc.

Note also that there will be no lab on Tuesday.

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Old exam 2

We have posted a previous exam 2 to give you some idea of what to expect on the up-coming test.

Olin & David

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Review session on Saturday

Spencer Small will be conducting a review session on Saturday, 6-9 PM, in International Village, room 22.

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Last-chance partner swap

We're offering a special deal, good for the next 24 hours.

Everyone has now worked with their new November/December partner. If it's not working out and you'd prefer a different partner, you may send us mail (to shivers+newpartner@ccs.neu.edu) requesting one; we'll pair you up with one of the other requestors.

We'll even accomodate specific requests: if you've got a specific person in mind with whom you'd like to work, say so and make sure that specific person sends us mail requesting you.

We'll collect all email requests received by Noon Thursday 2009/11/19 and process them.

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Extension on homework 8h

The geocode teachpack triggers an interesting bug in the handin server; we've just fixed it.

As a result, we're extending honor-section assignment 8 twelve hours—that is, to 8:00 AM Wednesday 11/18.

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Extension on homework 8h

The geocode teachpack triggers an interesting bug in the handin server; we've just fixed it.

We're extending honor-section assignment 8 twelve hours—to 8:00 AM Wednesday 11/18.

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Evaluator code (Honors), revisited

Here is the second and third pass of the meta-circular evaluator we built in class.

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Problem Set 9 (Regular)

The due date for problem set 9 has been pushed back 24 hours to 11/18.

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Evaluator code (Honors)

Here is the first pass of the meta-circular evaluator we built in class.

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Office hours this Wednesday 11/11

Profs. Shivers and Van Horn will be in all-day meetings on Wednesday, so will not have office hours. Students wishing to schedule time with them this week should send email to find alternate times.

Dan Brown, however, will be available this Wednesday, 12:30-2:30.

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November/December homework partner assignments

Here are the final partner assignments for the course.

 Aaron Gallaway (gallaway@ccis.neu.edu) and Kiril Geshev (geshevk@gmail.com) Alex Tironati (tironati.a@husky.neu.edu) and Alexander Sullivan (alexsullivan114@yahoo.com) Alexander Sullivan (alexsullivan114@yahoo.com) and Alex Tironati (tironati.a@husky.neu.edu) Alison Leibowitz (leibowitz.a@husky.neu.edu) and Madeleine Vaudo (vaudo.m@neu.edu) Andrew Anastor (anastor.a@neu.edu) and Jonathan Gallagher (gallagher.jon@husky.neu.edu) Andrew Benz (benz.a@neu.edu) and Vicky Wei (wei.v@husky.neu.edu) Andrew Nader (nader.a@husky.neu.edu) and Kyle Phelps (phelps.ky@husky.neu.edu) Angelo Coelho (coelho.a@husky.neu.edu) and Christian Germano (germano.c@husky.neu.edu) Ari Entlich (atrigent@ccs.neu.edu) and Jennifer Lehmann (lehmann.j@neu.edu) Arin Hunter-Schlorholtz (hunter-schlorholtz.a@husky.neu.edu) and Michael Nickerson (nickerson.mi@neu.edu) Brandon Lerner (lerner.b@husky.neu.edu) and Nathaniel Bessa (nbessa@ccs.neu.edu) Brendan Dwyer (BBdPuck222@gmail.com) and Ryan Schwers (schwers.r@husky.neu.edu) Brett Van Dorn (vandOrn.B@husky.neu.edu) and chris avenant (avenant.c@neu.edu) Brian Dedonato (dedonato.b@neu.edu) and Robert Grodin (grodin.r@husky.neu.edu) Brittany Waitte (waitte.b@husky.neu.edu) and Lauren Byrnes (Lbyrnes13@gmail.com) Charles Connell (cconnell@ccs.neu.edu) and Zachary Fand (fand.z@husky.neu.edu) Chris Avenant (avenant.c@neu.edu) and Brett Van Dorn (vandorn.b@husky.neu.edu) Chris Baldauf (baldauf.c@husky.neu.edu) and Lively Lively (perlive@ccs.neu.edu) Chris Jordan (jordan.chri@husky.neu.edu) and Chris Welden (chriswelden@gmail.com) Chris Shea (shea.ch@husky.neu.edu) and Nicki Beaudry (beaudry.n@husky.neu.edu) Chris Welden (chriswelden@gmail.com) and Chris Jordan (jordan.chri@husky.neu.edu) Christian Germano (germano.c@husky.neu.edu) and Angelo Coelho (coelho.a@husky.neu.edu) Christopher Jelly (jelly.c@husky.neu.edu) and Dorian Kersch (kersch.d@neu.edu) Christopher Mcgroarty (mcgroarty.c@husky.neu.edu) and Jason Shrand (shrand.j@neu.edu) Christopher Souvey (souvey.c@husky.neu.edu) and Griffin Schneider (schneider.g@husky.neu.edu) Courtney Sims (sims.c@husky.neu.edu) and Quinn Sissler (sissler.q@husky.neu.edu) Craig Berry (berry.cr@husky.neu.edu) and Thang Nguyen (thang@ccs.neu.edu) Daniel Brown (brown.daniel3@husky.neu.edu) and Thomas Higgins (tayhota@hotmail.com) Daniel Jin (jin.d@husky.neu.edu) and Wanfung Lee (lee.wanf@husky.neu.edu) Daniel Setrin (danset@comcast.net) and Pedro Lopes (lopes.p@husky.neu.edu) David Thor (thor.d@neu.edu) and Kevin Rottman (rottman.k@husky.neu.edu) Demitry Toumilovich (toumilovich.d@neu.edu) and Lee Tirrell (tirrell.le@neu.edu) Dorian Kersch (kersch.d@neu.edu) and Christopher Jelly (jelly.c@husky.neu.edu) Duncan Macleod (macleod.du@husky.neu.edu) and Ryan Haines (ryan.a.haines@gmail.com) Edwin Morris (edwin.h.morris@gmail.com) and Paul Murray (murray.pa@neu.edu) Emma Youndtsmith (alukewarmcase22@gmail.com) and Zane Whitney (whitneyz@ccs.neu.edu) Ghadir Alibrahim (alibrahim.g@neu.edu) and Yasmin Aljedawi (aljedawi.y@husky.neu.edu) Griffin Schneider (schneider.g@husky.neu.edu) and Christopher Souvey (souvey.c@husky.neu.edu) Henry Hines (hines.h@husky.neu.edu) and Jose Raul Lopez (chelelopez@hotmail.com) Ian Bird (bird.i@husky.neu.edu) and Tim Schuch (tschuch19@yahoo.com) Ian Mabie (ian.mabie@gmail.com), Michael Allen (allen.mic@husky.neu.edu) and Michael Murray (murray.mich@husky.neu.edu) Ian Oo (ianoo@ccs.neu.edu) and Ryan Maxim (maxim.r@husky.neu.edu) Jacob Hilker (hilker.j@husky.neu.edu) and Lori Monteleone (lmonte@ccs.neu.edu) James Pellerano (pellerano.j@husky.neu.edu) and Thomas Cardran (cardran.t@husky.neu.edu) James Shargo (shargo.j@huskey.neu.edu) and Robert Zych (zychjoe@ccs.neu.edu) Jason Pollock (jpoll8520@gmail.com) and Kyle Hodge (hodge.k@husky.neu.edu) Jason Shrand (shrand.J@Neu.edu) and Christopher McGroarty (mcgroarty.c@husky.neu.edu) Jennifer Lehmann (lehmann.j@neu.edu) and Ari Entlich (atrigent@ccs.neu.edu) Jennifer Simons (simons.jen@husky.neu.edu) and Zachary Johnson (johnson.za@husky.neu.edu) Jeroen Van Bockel (vanbockel.j@neu.edu) and Thomas Meng (meng.t@husky.neu.edu) Joel Yamasaki (yamasaki@ccs.neu.edu) and Scott Ryder (scott14@ccs.neu.edu) Jonathan Gallagher (gallagher.jon@husky.neu.edu) and Andrew Anastor (anastor.a@neu.edu) Jonathan Lane (jlane09sjp@gmail.com) and King Leung (leung.ki@neu.edu) Jonathan Millman (millmanorama@gmail.com) and Nathan Heaps (heaps.n@husky.neu.edu) Jose Raul Lopez (chelelopez@hotmail.com) and Henry Hines (hines.h@husky.neu.edu) Junhoi Kim (kim.ju@husky.neu.edu) and Sam Doyle (doyle.sa@neu.edu) Justin Yang (justinyang2264@gmail.com) and Nathaniel Smith (Smith.nat@husky.neu.edu) Kevin Rottman (rottman.k@husky.neu.edu) and David Thor (thor.d@neu.edu) King Leung (leung.ki@neu.edu) and Jonathan Lane (jlane09sjp@gmail.com) Kiril Geshev (geshevk@gmail.com) and Aaron Gallaway (gallaway@ccis.neu.edu) Kyle Hodge (hodge.k@husky.neu.edu) and Jason Pollock (jpoll8520@gmail.com) Kyle Maguire (gamemakerkyle@aol.com) and Tyler Rosini (rosini.t@neu.edu) Kyle Oestreich (oestreich.k@neu.edu) and Matt Gowie (gowie.m@neu.edu) Kyle Phelps (phelps.ky@husky.neu.edu) and Andrew Nader (nader.a@husky.neu.edu) Lauren Byrnes (Lbyrnes13@gmail.com) and Brittany Waitte (waitte.b@husky.neu.edu) Lee Tirrell (tirrell.le@neu.edu) and Demitry Toumilovich (toumilovich.d@neu.edu) Leigh Scorza (scorza.l@husky.neu.edu) and Regina Ranstrom (ranstrom.r@husky.neu.edu) Lindsay Houck (houck.l@husky.neu.edu) and Nikko Patten-Weinstein (nikkopatten@gmail.com) Lively Lively (perlive@ccs.neu.edu) and Chris Baldauf (baldauf.c@husky.neu.edu) Lori Monteleone (lmonte@ccs.neu.edu) and Jacob Hilker (hilker.j@husky.neu.edu) Louis Coyle (lhcoyle4@gmail.com) and Michael Becker (becker.mi@husky.neu.edu) Madeleine Vaudo (vaudo.m@neu.edu) and Alison Leibowitz (leibowitz.a@husky.neu.edu) Matt Gowie (gowie.m@neu.edu) and Kyle Oestreich (oestreich.k@neu.edu) Michael Allen (allen.mic@husky.neu.edu), Ian Mabie (ian.mabie@gmail.com) and Michael Murray (murray.mich@husky.neu.edu) Michael Becker (becker.mi@husky.neu.edu) and Louis Coyle (lhcoyle4@gmail.com) Michael Murray (murray.mich@husky.neu.edu), Michael Allen (allen.mic@husky.neu.edu) and Ian Mabie (ian.mabie@gmail.com) Michael Nickerson (nickerson.mi@neu.edu) and Arin Hunter-Schlorholtz (hunter-schlorholtz.a@husky.neu.edu) Michael Saccone (mrsaccone@yahoo.com) and Ryan Donahue (donahue.rya@husky.neu.edu) Nader Sassani (nsassani@gmail.com) and Nicholas Stapczynski (stapczynski.n@husky.neu.edu) Nathan Heaps (heaps.n@husky.neu.edu) and Jonathan Millman (millmanorama@gmail.com) Nathaniel Bessa (nbessa@ccs.neu.edu) and Brandon Lerner (lerner.b@husky.neu.edu) Nathaniel Smith (Smith.nat@husky.neu.edu) and Justin Yang (justinyang2264@gmail.com) Nelson Man (man.n@husky.neu.edu) and Regan Yee (regannn@gmail.com) Nguyen Nguyen (nguyen.ngu@husky.neu.edu) and Poon Edmond (edpoon@ccs.neu.edu) Nicholas Stapczynski (stapczynski.n@husky.neu.edu) and Nader Sassani (nsassani@gmail.com) Nicki Beaudry (beaudry.n@husky.neu.edu) and Chris Shea (shea.ch@husky.neu.edu) Nikko Patten-Weinstein (nikkopatten@gmail.com) and Lindsay Houck (houck.l@husky.neu.edu) Oluwasegun Odedele (madamada21@gmail.com) and Qimeng Song (song.q@husky.neu.edu) Paul Murray (murray.pa@neu.edu) and Edwin Morris (edwin.h.morris@gmail.com) Pedro Lopes (lopes.p@husky.neu.edu) and Daniel Setrin (danset@comcast.net) Pengyu Li (li_pengyu@yahoo.com) and Wensheng Mao (maowensheng@hotmail.com) Poon Edmond (edpoon@ccs.neu.edu) and Nguyen Nguyen (nguyen.ngu@husky.neu.edu) Qimeng Song (song.q@husky.neu.edu) and Oluwasegun Odedele (madamada21@gmail.com) Quinn Sissler (sissler.q@husky.neu.edu) and Courtney Sims (sims.c@husky.neu.edu) Regan Yee (regannn@gmail.com) and Nelson Man (man.n@husky.neu.edu) Regina Ranstrom (ranstrom.r@husky.neu.edu) and Leigh Scorza (scorza.l@husky.neu.edu) Richard Pruitt (rpruitt@ccs.neu.edu) and Scott Surette (surette@ccs.neu.edu) Robert Grodin (grodin.r@husky.neu.edu) and Brian Dedonato (dedonato.b@neu.edu) Robert Zych (zychjoe@ccs.neu.edu) and James Shargo (shargo.j@huskey.neu.edu) Ryan Donahue (donahue.rya@husky.neu.edu) and Michael Saccone (mrsaccone@yahoo.com) Ryan Haines (ryan.a.haines@gmail.com) and Duncan Macleod (macleod.du@husky.neu.edu) Ryan Maxim (maxim.r@husky.neu.edu) and Ian Oo (ianoo@ccs.neu.edu) Ryan Schwers (schwers.r@husky.neu.edu) and Brendan Dwyer (BBdPuck222@gmail.com) Sam Doyle (doyle.sa@neu.edu) and Junhoi Kim (kim.ju@husky.neu.edu) Scott Ryder (scott14@ccs.neu.edu) and Joel Yamasaki (yamasaki@ccs.neu.edu) Scott Surette (surette@ccs.neu.edu) and Richard Pruitt (rpruitt@ccs.neu.edu) Thang Nguyen (thang@ccs.neu.edu) and Craig Berry (berry.cr@husky.neu.edu) Thomas Cardran (cardran.t@husky.neu.edu) and James Pellerano (pellerano.j@husky.neu.edu) Thomas Higgins (tayhota@hotmail.com) and Daniel Brown (brown.daniel3@husky.neu.edu) Thomas Meng (meng.t@husky.neu.edu) and Jeroen Van Bockel (vanbockel.j@neu.edu) Tim Schuch (tschuch19@yahoo.com) and Ian Bird (bird.i@husky.neu.edu) Tyler Rosini (rosini.t@neu.edu) and Kyle Maguire (gamemakerkyle@aol.com) Vasily Pekurovsky (pekurovsky.v@husky.neu.edu) and Xiaodong Lu (lu.xi@neu.edu) Vicky Wei (wei.v@husky.neu.edu) and Andrew Benz (benz.a@neu.edu) Wanfung Lee (lee.wanf@husky.neu.edu) and Daniel Jin (jin.d@husky.neu.edu) Wensheng Mao (maowensheng@hotmail.com) and Pengyu Li (li_pengyu@yahoo.com) Xiaodong Lu (lu.xi@neu.edu) and Vasily Pekurovsky (pekurovsky.v@husky.neu.edu) Yarian Gomez (gomez.ya@husky.neu.edu) and Yury Olshansky (olshansky.y@neu.edu) Yasmin Aljedawi (aljedawi.y@husky.neu.edu) and Ghadir Alibrahim (alibrahim.g@neu.edu) Yury Olshansky (olshansky.y@neu.edu) and Yarian Gomez (gomez.ya@husky.neu.edu) Zachary Fand (fand.Z@Husky.neu.edu) and Charles Connell (cconnell@ccs.neu.edu) Zachary Johnson (johnson.za@husky.neu.edu) and Jennifer Simons (simons.jen@husky.neu.edu) Zane Whitney (whitneyz@ccs.neu.edu) and Emma Youndtsmith (alukewarmcase22@gmail.com)

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November/December partners, part II

Zane has requested that you not send him email. Rather, he has created a "pair-requests" assignment, which you can see from the handin system in your Dr. Scheme. New partner pairs should submit a file (whose contents will be ignored) as the pair to be registered for the final pairing.

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November/December partners

It's time to pick your final partner for November and December. You can submit your partner choice to your TA at your lab session, or email it to Zane (zane@ccs.neu.edu).

Alternatively, you can do nothing–if we don't have a partner request from you by Wednesday morning 8:00 AM, we'll assign you someone at random.

Snake code

The source code for the complete snake game is now available.

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Extension on homework 6

In response to concerted, wide-spread grovelling and wailing, we are moving the deadline for homework 6 back 1 day, to Tuesday 8:00 pm.

This a one-shot deal; there will surely be no further extensions on other homework assignments.

In other xml-related advice, "counting the number of characters in an Xexpr" means to sum up the length of all the strings in the Xexpr -- the symbol tags don't contribute anything to the count.

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RSS Feed for Blog

Your fearless head TA, Zane Shelby, has set up an RSS feed for the course blog. Go forth and be informed about what's going on in CS2500.

http://www.feed43.com/cs2500f09.xml

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Assignment 5H due date moved AGAIN

The Assignment 5 Honors due date has been moved back again, this time to Wednesday 10/21 due to Handin server issues. The submission instructions have been changed; please refer to the assignment 5h write-up for details. (The important bits are in red.)

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Assignment 5H due date moved

The Assignment 5 Honors due date has been moved back to Tuesday 10/20 as discussed in class last Thursday.

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Blue on blue

In the military, "blue on blue" is an expression used when friendly forces get confused and fire on their own side.

In CS 2500, "blue on blue" is an expression used when your friendly professors get confused and order our forces to overlay text onto a background of identical color.

Homework 5 directs you to paint blue text onto a blue background. This will produce a fairly uninteresting result. We have corrected the assignment—please paint blue text onto a plain white background.

–The management

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Study Session

A study session, sponsored by the CCIS Peer Mentoring Group, is going to take place Friday in INV room 22 from 6:00-8:00pm for anyone who needs help studying for the upcoming exam. Mentors and tutors will be available to help you so stop by at any point with any questions you may have. Come prepared with questions.

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Test 1 details

The test will be held 6:30 PM – 9:30 PM, in 108 Snell Engineering this Monday (10/19), for students in all sections of the class.

The test will be open book: you can bring any kind of hardcopy you wish, including the textbook, notes, and printouts. You may not bring or use calculators, computers, cell phones, etc.

Note also that there will be no lab on Tuesday.

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Partial snake code

Here is the half-completed source code for the snake game we've been developing in class.

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Previous Exams

Here are some previous exams to help you prepare for Monday's test:

Exam 1, Fall 2008

Exam 1, Fall 2007

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Signature requirement relaxed

We've relaxed the requirement on problem A1 of regular-track homework 4. You may ask any tutor for a signature, not just the one who graded your last homework.

October partners

Just a reminder that your must work with your new October partner for October. If you liked working with your September partner, you may continue to discuss the homework with that person, but you cannot program with that person, or look at that person's code, or otherwise share code.

We plan to let students repeat partners in December, so consider the September/October/November partner shuffling as a good reconaissance opportunity for your December request...

No lab before Thanksgiving

As the TAs and instructors will be locked in a room grading midterm 2 all day on Tuesday November 24, there will be no lab on that day. This may be of utility to those of you making travel plans for the Thanksgiving holiday.

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Homework 4 is up

Homework 4 for the regular track is up on the course web site; it is due in at 8:00 this Saturday 10/10. You do this one with your new October partner.

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October partner assignments

Here are the partner assignments for October. You may work with your September partner for any assignment due in before this Thursday or with your November partner, but you can only work with one other person, no matter which choice you make.

 Al ibrahim, Ghadir J. & DiBenedetto, Pio V. Aljedawi, Yasmin A. & Nguyen, Nguyen Allen, Michael W. & Cohenca, Jaime I. Anastor, Andrew & Cardran, Thomas P. Avenant, Christopher E. & Haines, Ryan Baldauf, Christopher D. & Nader, Andrew C. Beaudry, Nicole L. & Gallaway, Aaron D. Becker, Michael B. & Byrnes, Lauren E. Benz, Andrew A. & Wei, Victoria Berry, Craig C. & Coyle, Louis H. Bessa, Nathaniel B. & Youndtsmith, Emma J. Bird, Ian M. & Leung, King Fung Brown, Daniel & Van Bockel, Jeroen S. Byrnes, Lauren E. & Becker, Michael B. Campbell, Christopher T. & Zych, Robert J. Cardran, Thomas P. & Anastor, Andrew Coelho, Angelo K. & Yee, Regan W. Cohenca, Jaime I. & Allen, Michael W. Connell, Charles H. & Gowie, Matthew Coyle, Louis H. & Berry, Craig C. D'Amelio, Eleanor M. & Meyer, Eric J. Dedonato, Brian J. & Meng, Thomas DiBenedetto, Pio V. & Al ibrahim, Ghadir J. Donahue, Ryan R. & El Manzalawy, Mostafa O. Doyle, Sam K. & Lane, Jonathan E. Dwyer, Brendan J. & Odedele, Oluwasegun El Manzalawy, Mostafa O. & Donahue, Ryan R. Entlich, Ari G. & Jin, Daniel Fagan, James D. & Wessel, Erik A. Fand, Zachary A. & Lerner, Brandon Freed, Jason S. & Jelly, Christopher D. Gallagher, Jonathan & Lu, Xiaodong Gallaway, Aaron D. & Beaudry, Nicole L. Germano, Christian E. & Yang, Justin Gerweck, Zachary & Li, Pengyu Geshev, Kiril & Sassani, Nader Gloski, Troy V. & Sparacino, Holden S. Gomez, Yarian & Song, Qimeng Gowie, Matthew & Connell, Charles H. Grodin, Robert D. & Kim, Jun Hoi Haines, Ryan & Avenant, Christopher E. Hapil, Abigail P. & Millman, Jonathan Heaps, Nathan S. & Shrand, Jason A. Higgins, Thomas J. & Schuch, Timothy J. Hilker, Jacob W. & Monteleone, Lori L. Hines, Henry C. & Surette, Scott A. Hodge, Kyle & Lehmann, Jennifer A. Houck, Lindsay A. & Nordstrom, Wayne G. Hunter-Schlorholtz, Arin J. & Patten-Weinstein, Nikko A. Jelly, Christopher D. & Freed, Jason S. Jin, Daniel & Entlich, Ari G. Johnson, Zachary L. & Van Dorn, Brett Jordan, Christopher & Mao, Wensheng Kersch, Dorian J. & Lopez Arguello, Jose Raul Kim, Jun Hoi & Grodin, Robert D. Lane, Jonathan E. & Doyle, Sam K. Lee, Wanfung J. & Murray, Paul Lehmann, Jennifer A. & Hodge, Kyle Leibowitz, Alison & Vaudo, Madeleine S. Lerner, Brandon & Fand, Zachary A. Leung, King Fung & Bird, Ian M. Li, Pengyu & Gerweck, Zachary Lively, Perron A. & Pruitt, Richard I. Lopes, Pedro J. & Yamin, Arash Lopez Arguello, Jose Raul & Kersch, Dorian J. Lu, Xiaodong & Gallagher, Jonathan Mabie, Ian S. & Nguyen, Thang MacLeod, Duncan J. & Shea, Christopher R. Maguire, Kyle R. & Welden, Christopher Man, Nelson & Tozian, Tani M. Mao, Wensheng & Jordan, Christopher Matthews, John L. & Sullivan, Alexander L. Maxim, Ryan & Oo, Ian L. McGroarty, Christopher M. & Rottman, Kevin P. Meng, Thomas & Dedonato, Brian J. Meyer, Eric J. & D'Amelio, Eleanor M. Millman, Jonathan & Hapil, Abigail P. Monteleone, Lori L. & Hilker, Jacob W. Morris, Edwin H. & Schneider, Griffin C. Murray, Michael R. & Tirrell, Lee Murray, Paul & Lee, Wanfung J. Nader, Andrew C. & Baldauf, Christopher D. Nguyen, Minh Tam & Poon, Edmond T. Nguyen, Nguyen & Aljedawi, Yasmin A. Nguyen, Thang & Mabie, Ian S. Nickerson, Mike & Tironati, Alexander Nordstrom, Wayne G. & Houck, Lindsay A. Odedele, Oluwasegun & Dwyer, Brendan J. Oestreich, Kyle B. & Smith, Nathaniel K. Olshansky, Yury & Pollock, Jason R. Oo, Ian L. & Maxim, Ryan Patten-Weinstein, Nikko A. & Hunter-Schlorholtz, Arin J. Pekurovsky, Vasily & Whitney, Zane P. Pellerano, James A. & Ranstrom, Regina R. Phelps, Kyle W. & Simons, Jennifer L. Pollock, Jason R. & Olshansky, Yury Poon, Edmond T. & Nguyen, Minh Tam Pruitt, Richard I. & Lively, Perron A. Ranstrom, Regina R. & Pellerano, James A. Rao, India G. & Williams, Jennie J. Rosini, Tyler & Thor, David C. & Souvey, Christopher A. Rottman, Kevin P. & McGroarty, Christopher M. Ryder, Scott M. & Scorza, Leigh A. Saccone, Michael R. & Yamasaki, Joel C. Sassani, Nader & Geshev, Kiril Schneider, Griffin C. & Morris, Edwin H. Schuch, Timothy J. & Higgins, Thomas J. Schwers, Ryan J. & Shargo, James M. Scorza, Leigh A. & Ryder, Scott M. Setrin, Daniel J. & Stapczynski, Nicholas C. Shargo, James M. & Schwers, Ryan J. Shea, Christopher R. & MacLeod, Duncan J. Shrand, Jason A. & Heaps, Nathan S. Simons, Jennifer L. & Phelps, Kyle W. Sims, Courtney L. & Sissler, Quinn A. Sissler, Quinn A. & Sims, Courtney L. Smith, Nathaniel K. & Oestreich, Kyle B. Song, Qimeng & Gomez, Yarian Souvey, Christopher A. & Rosini, Tyler & Thor, David C. Sparacino, Holden S. & Gloski, Troy V. Stapczynski, Nicholas C. & Setrin, Daniel J. Sullivan, Alexander L. & Matthews, John L. Surette, Scott A. & Hines, Henry C. Thor, David C. & Souvey, Christopher A. & Rosini, Tyler Tironati, Alexander & Nickerson, Mike Tirrell, Lee & Murray, Michael R. Toumilovich, Demitry A. & Waitte, Brittany B. Tozian, Tani M. & Man, Nelson Van Bockel, Jeroen S. & Brown, Daniel Van Dorn, Brett & Johnson, Zachary L. Vaudo, Madeleine S. & Leibowitz, Alison Waitte, Brittany B. & Toumilovich, Demitry A. Wei, Victoria & Benz, Andrew A. Welden, Christopher & Maguire, Kyle R. Wessel, Erik A. & Fagan, James D. Whitney, Zane P. & Pekurovsky, Vasily Williams, Jennie J. & Rao, India G. Yamasaki, Joel C. & Saccone, Michael R. Yamin, Arash & Lopes, Pedro J. Yang, Justin & Germano, Christian E. Yee, Regan W. & Coelho, Angelo K. Youndtsmith, Emma J. & Bessa, Nathaniel B. Zych, Robert J. & Campbell, Christopher T.

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Russian Doll code

Here is the code from our lecture on Russian dolls:

 ;; An RD is one of: ;; - 'solid ;; - (make-shell RD) (define-struct shell (guts)) ;; layers : RD -> Number ;; Count the number of shells. #; (define (rd-template d) (cond [(symbol? d) ...] [(shell? d) (rd-template (shell-guts d)) ...])) (check-expect (layers 'solid) 0) (check-expect (layers (make-shell 'solid)) 1) (check-expect (layers (make-shell (make-shell 'solid))) 2) (define (layers d) (cond [(symbol? d) 0] [(shell? d) (add1 (layers (shell-guts d)))]))

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New partners

October means new homework partners. If you have someone in mind with whom you would like to work, send your new partner request to shivers+partner@ccs.neu.edu . If you don't have a partner in mind, we can assign you one.

Students have until midnight Friday night (10/2) to send us partner requests. Then we'll take everyone else and randomly partner them up for October.

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Second-edition HtDP

The authors of the course text How to Design Programs have put the current draft of the second edition online. It has an improved variant of the world teachpack, called the universe teachpack, that you might want to check out.

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Desireable lab slot

The Tuesday 5:15-6:55 lab is quite undersubscribed (it currently has about 5 students). If you can move from your current lab to this time slot, you will get great interaction with the TAs and tutors teaching it. Send David or Olin email if you would like to shift.

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Assignment 2h

Assignment 2 for the honors section has been posted on the web site.

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