CS2500 Blog

The End

Tue, 04 May 2010 13:21:26 -0400

We’re done! Thanks for a great semester.

I’m supposed to once again encourage you to complete TRACE online course evaluation surveys. They’ve extended the deadline. You can get to them from myNEU. Don’t forget to fill out the survey for the lab course (CS2501) and your TAs Stevie and Vincent.

Enjoy your summer and keep programming.

Don’t Forget Your Late Days

Mon, 19 Apr 2010 19:15:23 -0400

If you have late days remaining, you can certainly use them on Problem Set 12—just let Stevie know before it’s due. As usual, you can use a maximum of two, so no games will be accepted after 11:59 PM on Thursday.

TRACE Surveys

Fri, 16 Apr 2010 12:54:34 -0400

I’m supposed to encourage you to complete TRACE online course evaluation surveys. These are different from the surveys you did yesterday in class. The survey will be open until May 2 at 11 PM.

Updated Lecture Notes

Thu, 15 Apr 2010 20:39:49 -0400

Wednesday’s and today’s lecture notes, combined.

Lecture Notes

Wed, 14 Apr 2010 21:03:46 -0400

I’ve posted lecture notes for Monday and Wednesday.

Proposals Now Due Tuesday

Sat, 10 Apr 2010 14:02:31 -0400

I’ve received only one game proposal thus far, and this has me worried. Proposals are now due this Tuesday, 4/13, at 11:59 PM. Don’t try to submit them using the submission server—please email them to me.

Partner Reminder and Lecture Notes

Fri, 09 Apr 2010 13:30:23 -0400

Several partner requests have now been fulfilled. If you still need a partner, please email me ASAP.

I’ve posted lecture notes for Wednesday (optional lecture) and Thursday.

Lab Quiz Amnesty

Thu, 08 Apr 2010 02:42:45 -0400

When you get back your exam, you may notice a list of lab numbers at the bottom. If you have such a list, these are the lab quizzes that you missed or failed over the course of the semester. Our rule is that you can only receive credit for your homework in weeks where you pass or make up your lab quiz. Therefore, if you have missing or failing quiz grades, this could severely impact your grade.

Since we want you to get credit for the work that you did, we are announcing a lab quiz amnesty. For one week only, starting at Vincent’s office hours on Friday and continuing through Jesse’s on Monday and Stevie’s on Tuesday, you may make up any quizzes that you have missed.

Some guidelines:

Show up at least half an hour before the end of office hours if you want to be sure we’ll have time to give you a quiz.
Don’t expect this to be easy. We try to help you quite a bit during regular quiz make-ups, but for this we’ll be a little tougher.
If you can’t make any of the three available office hour periods over the next week, please email to make an appointment.

No Lab Tomorrow/Today, but Yes Lecture

Wed, 07 Apr 2010 22:07:53 -0400

Don’t forget that lab is canceled tomorrow. We won’t be there. We do still have lecture, though. Come get your exams and learn about accumulators.

Problem Set 12 Is Up

Wed, 07 Apr 2010 20:24:12 -0400

Problem Set 12.

Start now, because you need to have your proposal approved before you start coding. If you need a partner, please email ASAP.

Review Session Notes

Wed, 07 Apr 2010 12:03:51 -0400

Several people have asked for these notes from the review session.

Fractals in HTDP

Sun, 04 Apr 2010 00:46:21 -0400

Several of you have asked me questions about the fractal code in §27.1 of HTDP and how it might relate to your homework. The idea of generative recursion is the same, but the code in the book uses the draw.ss teachpack, which works very differently from the image.ss and universe.ss teachpacks that we use now.

In particular, the draw.ss teachpack relies on side effects. A side effect is when calling a function, in addition to returning some answer, causes something to happen. In this particular teachpack, for example, there is a line function that always returns true, but also causes a line to appear on the screen. Everything we do using the image.ss teachpack is about returning images, not about causing things to happen on the side. (Even when you use big-bang, all the functions you write are about computing values, not doing things. Things happen, but that’s something that big-bang takes care of for you.)

Rather than using side effects, you should be writing a function that returns a scene. You can make this work if you think carefully about the four parts in the recipe for generative recursion:

What is a trivial problem? Is there some size fractal that you can produce right away, without recursion? In particular, is there some size under which smaller sizes could not show additional detail?
How do you produce this trivial fractal?
For a larger fractal, how can you generate a simpler (smaller) subproblem, which you can then solve recursively?
How can you construct the fractal you want from the solution to the smaller problem?

Since it might help, let’s take a look at the function sierpinski from the book:

;; sierpinski : posn posn posn  ->  true
;; to draw a Sierpinski triangle down at a, b, and c,
;; assuming it is large enough
(define (sierpinski a b c)
  (cond
    [(too-small? a b c) true]
    [else 
     (local [(define a-b (mid-point a b))
             (define b-c (mid-point b c))
             (define c-a (mid-point a c))]
       (and
         (draw-triangle a b c)
         (sierpinski a a-b c-a)
         (sierpinski b a-b b-c)
         (sierpinski c c-a b-c)))]))

You can see in the first cond clause, it checks for the trivial case (too-small? a b c), and the trivial solution is to draw nothing else to the screen, so it returns true. Otherwise, it uses and to sequence four side-effecting operations: First it draws a triangle at the requested points on the screen, and then it recurs three times to draw the subfractals (subproblems) to the screen. This is following the recipe for generative recursion, but in terms of drawing, it is quite different from how we do things.

For comparison, here’s a version that’s closer to how we do it in this course. Notice the changes to the contract and purpose:

;; sierpinski-helper : Posn Posn Posn Scene -> Scene
;; To add a Sierpinski triangle at points a, b, and c
;; to the given scene, assuming it is large enough to see
(define (sierpinski a b c scene)
  (cond
    [(too-small? a b c) scene]
    [else 
     (local [(define a-b (mid-point a b))
             (define b-c (mid-point b c))
             (define c-a (mid-point a c))]
       (sierpinski c c-a b-c
        (sierpinski b a-b b-c
         (sierpinski a a-b c-a
          (add-triangle a b c scene)))))]))

If you’d like to make this work, you’ll need to write too-small? : Posn Posn Posn -> Boolean and add-triangle : Posn Posn Posn Scene -> Scene.

Note that if you want to use a similar strategy for sierpinski-carpet, the recursive function had to be a helper to a Natural -> Scene function that creates the empty scene and calls the helper to add the carpet to it.

Graph Coloring Lecture Notes

Sat, 03 Apr 2010 20:46:12 -0400

Lecture notes from Thursday.

Exam Review Session

Fri, 02 Apr 2010 14:44:21 -0400

The review session will be held on Monday from 6 to 8 PM in 272 West Village F. I haven’t been there, but I expect it’s just upstairs from our usual lecture room.

Topological Sort Lecture Notes

Wed, 31 Mar 2010 23:33:22 -0400

Lecture notes from today.

Practice Exam

Wed, 31 Mar 2010 16:27:11 -0400

Here’s a practice exam for next week’s midterm.

Even More Lecture Notes

Tue, 30 Mar 2010 12:37:41 -0400

Lecture notes from Wednesday 2/14 and Monday 3/29.

Lecture Notes

Thu, 18 Mar 2010 10:19:07 +0100

Lecture notes from Monday and Wednesday.

Instructor Office Hours Schedule

Sat, 13 Mar 2010 07:48:55 -0500

Because I’ll be out of town, I won’t have my usual office hours on 3/15, 3/22, and probably 3/29. I will hold office hours on Monday, 3/15, from 11:30 AM to 1:30 PM, and again on Tuesday, 3/30, from 2 to 4 PM, both in my office (308 WVH). I’ll resume the usual schedule on Monday, 4/5.

Lecture Notes and the Make-Up Quiz

Fri, 12 Mar 2010 09:57:24 -0500

Here is the code from Wednesday and Thursday.

I’ve been asked to post the make-up quiz from class yesterday, so here it is. (The solution is in white text. To see it, either highlight it or copy it and paste in another program.)

;; A QTree is one of:
;; – "Q"
;; – (make-single QTree)
;; – (make-double QTree QTree)
;; – (make-triple QTree QTree QTree)
(define-struct single (only))
(define-struct double (this that))
(define-struct triple (left middle right))
 
;; Template for QTree:
(define (process-qtree qt)
  (cond
    [(string? qt)   ...]
    [(single? qt)   ... (process-qtree (single-only qt)) ...]
    [(double? qt)   ... (process-qtree (double-this qt)) ...
                    ... (process-qtree (double-that qt)) ...]
    [else           ... (process-qtree (triple-left qt)) ...
                    ... (process-qtree (triple-middle qt)) ...
                    ... (process-qtree (triple-right qt)) ...]))
 
;; q-count : QTree -> Natural
;; To count the number of "Q"s in a QTree.
(define (q-count qt)
  (cond
    [(string? qt)   1]
    [(single? qt)   (q-count (single-only qt))]
    [(double? qt)   (+ (q-count (double-this qt))
                       (q-count (double-that qt)))]
    [else           (+ (q-count (triple-left qt))
                       (q-count (triple-middle qt))
                       (q-count (triple-right qt)))]))
 
;; Examples/Tests:
(check-expect (q-count "Q") 1)
(check-expect (q-count (make-double (make-single "Q") "Q"))
              2)
(check-expect (q-count (make-triple
                        (make-double "Q" "Q")
                        (make-single (make-single "Q"))
                        "Q"))
              4)

Monday’s Lecture Notes

Wed, 10 Mar 2010 20:07:31 -0500

Here is the code from Monday.

Frequent Design Doc Advice

Tue, 09 Mar 2010 10:00:18 -0500

Having written some of the same comments several times in response to the design documents turned in so far, I figured I could save us all some trouble by sharing them with the rest of you now, while you’re still working on yours.

Storing a velocity in your representation of an enemy (or shot) implies that the velocity will be different for different enemies (or shots) or at different times. Above, you included those velocities in your list of constants, but you’re also including velocities in your data representation. Which is it? Storing the same constant everywhere for some value that doesn’t change just makes your code more complex.
Your list of functions is a good start, but you may want to think this through a bit more before you start coding.

Most of your contracts just take worlds to worlds, but I’m certain you’ll actually have many functions that deal with only part of the world.

Might you want some rendering helpers or helpers for generating new enemies?
Hint: Use place-image to add each enemy (and shot) to the scene. Avoid overlay/xy. Trying to assemble several different scene elements by overlaying them before adding them to the world will just cause you trouble.
You aren’t sure yet how you’ll do collision detection. You may benefit from the concept of a bounding box. The displayed shape of a thing might be complicated, but as long as it’s pretty small (enemies and bullets both count), for collision detection it’s often best to treat it as a rectangle. It’s very easy to tell when two rectangles overlap. If you have two rectangles centered at (x₁, y₁) and (x₂, y₂), with dimensions w₁ by h₁ and w₂ by h₂, then they overlap when x₁ and x₂ are no more than (w₁ + w₂) / 2 apart and y₁ and y₂ are no more than (h₁ + h₂) / 2 apart.

Circles and points are good, too. It’s very easy to tell when a point intersects a circle, a circle intersects a circle, or a point intersects a rectangle.
Be careful not to write helpers that you may turn out not to need, or to need with a substantially different interface.
Random enemy generation is hard; I found it to be the hardest part. I’d recommend doing it near the end. Before that, you can use a hand-made list of enemies that you make yourself.

Email Me if You’re Missing Class Today

Mon, 08 Mar 2010 13:55:32 -0500

If you are 1) still in the class and 2) missing lecture today, please email me by the end of class today to tell me. This will ensure that you are assigned a partner. (Conversely: If you miss lecture today and don’t email me, I’ll assume you are withdrawing and may not assign you a partner.)

New Partners

Sun, 07 Mar 2010 17:17:03 -0500

If you haven’t requested a new partner yet, and you want to have some say in who you work with, email me ASAP!

(Also, I’d be glad to start looking over your game designs now if you send them to me.)

Problem Set 6 Solutions

Sun, 28 Feb 2010 00:12:06 -0500

Some of you asked me for solutions to last week’s homework.

Design Document from Today’s Lecture

Thu, 25 Feb 2010 21:48:08 -0500

Here is today’s lecture code, which includes my design document for the ball world program.

Also, something I neglected to mention today, which you may need rather soon, is the ‘function’ random. I put ‘function’ in quotes there because unlike every Scheme function we’ve seen so far, random may return different results when given the exact same arguments. It’s not truly a function in the mathematical sense, but it’s useful for what we want to do in Scheme.

New Late Day Rules

Thu, 25 Feb 2010 00:50:00 -0500

For the rest of this course, you have four free late days to be used as you wish, according to the following rules:

To use a late day, email Jesse and Stevie before the time that the homework is due.
If you tell us that you’re using one late day and need to use a second, you must tell us before your first late day ends.
You may use at most two late days for any one assignment.
When you use a late day, you get a 24 hour extension, until 11:59 PM the next day.
We will be leaving electronic submission open for 48 hours after each homework is due. To submit late, submit electronically before your late day (or two late days, if you so choose) ends.
You and your partner must use a late day together. If one partner has no late days remaining but the other has two, the partner that has two needs to email us to confirm that he or she wishes to give a late day to the partner that has none.

Caution: Since we now need to leave the hand-in server open beyond the normal due date, there are a few things to watch out for. In particular, at some point after the due date, but possibly before the late days end, we may gather your homework and begin grading. This means that if you intend to take a late day but you don’t tell us, we won’t know to wait to grade your homework, so we may grade a previous submission that you’ve sent us on time—but we might not, depending on when we start grading. On the other hand, if you submit late but don’t tell us, we might assume you intended to take a late day and charge you for it.

I realize that’s quite a few rules, but I hope this will make the course fairer and make it easier for you to deal with unforseen obstacles. I suggest conserving your late days for dire circumstances, because if you run out, you might not have them when you really need them.

Today’s Lecture Code (updated)

Thu, 25 Feb 2010 00:24:53 -0500

Here is today’s lecture code.

Today’s Lecture Code

Mon, 22 Feb 2010 21:25:07 -0500

Here is today’s lecture code.

Alpaca Birthdays

Mon, 22 Feb 2010 16:08:21 -0500

For problem 4, you may safely assume that no two alpacas were born on the same day.

For this homework assignment, using the right template for processing alpacas will be a great help in getting your code to work. If at any point you find yourself thinking about alpacas’ grandparents, writing phrases like (alpaca-dam (alpaca-dam a)), this is a sign that you need some recursion. (Follow the shape of the data definition!)

If you find yourself writing things like (alpaca-dob (alpaca-sire a)), that indicates the need for a helper function.

Lecture Notes from Thursday

Sat, 20 Feb 2010 23:37:05 -0500

Here.

Problem Set 6

Thu, 18 Feb 2010 12:53:38 -0500

Problem Set 6 is posted—enjoy!

Lecture Notes from Today

Wed, 17 Feb 2010 17:45:30 -0500

By request, today’s lecture notes.

How to Know if You Know Enough about Recursion

Sun, 14 Feb 2010 15:48:40 -0500

Can you:

make data definitions for lists of different things?
write the templates for those data definitions?
find the length of a list?
combine all the elements of a list using some operation, for example sum a list of numbers or append a list of strings?
change all the elements of a list in the same way, for example add some number n to every number in a list or find the length of every string in a list?
filter a list for elements with some property, for example keep only the numbers greater than some number n?
combine some of the above, for example sum all the numbers greater than n?

These are the essential ideas behind everything we’ve seen done with lists thus far. If you can do these and you can recognize variations on these themes, you should be in good shape.

Office Hours Monday by Appointment Only

Fri, 12 Feb 2010 15:37:33 -0500

Due to the Monday holiday, regular office hours (Christopher’s, Nikko’s, and mine) are cancelled. However, I will be available by appointment on both Monday and Tuesday. I’ll be glad to meet with any of you given 24 hours’ notice.

Exam Location, Review Session, and Study Materials

Fri, 12 Feb 2010 13:42:35 -0500

The midterm exam will be on Wednesday, February 17, from 6:30 to 9:30 PM, in 335 Shillman Hall. Shillman is building 30 in the lower-right corner of this map, just north of Centennial Common.
The review session will be on Monday, February 15, from 8 to 10 PM, in 366 West Village H. Take the elevator to the third floor, go right out of the elevator, turn right again when you hit the windows, and 366 will be on your right.
In case you missed them before, here are the practice exams from Fall 2007 and Fall 2008.
We have lecture code from yesterday.

New Partners!

Wed, 10 Feb 2010 18:46:00 -0500

I just sent emails informing you of your new partners for Problem Set 5. Please let me know if you didn’t get yours.

Some people find pair programming effective and others less so. We require you to do it in this course because we’ve found that it’s an effective way to learn, and we require you to switch partners because we want you to experience working with different people and working with people you don’t know. In case you’re interested, here’s an article about what makes pair programming effective.

Early Bird Lab and Partner Clarification

Wed, 10 Feb 2010 15:46:46 -0500

Some of you have been asking me who you should do Problem Set 5 with. The answer is: You don’t know yet, but you will very soon. I’ll be emailing you this afternoon, as soon as I work out who partners will be.

I’ve posted Lab 5 early for those of you that might want to get started today. If you find you’re having a hard time finishing the labs, starting early might help.

No Class

Wed, 10 Feb 2010 11:33:48 -0500

On the miniscule chance that you are reading this course blog but haven’t yet heard from another source, Northeastern has cancelled classes meeting after noon today. That includes ours.

Problem Set 5 and Practice Exams

Tue, 09 Feb 2010 23:34:06 -0500

Hello all! I’ve posted Problem Set 5 and practice exams from Fall 2007 and Fall 2008.

Today’s Code

Mon, 08 Feb 2010 21:52:37 -0500

Here’s the lecture code from today.

Typo in PS4

Mon, 08 Feb 2010 00:21:11 -0500

I just corrected a mistake in Problem Set 4. The last word of Problem 1 said “code” where it should say “cond.&rdquo.

Partner Requests

Sun, 07 Feb 2010 11:54:06 -0500

If you haven’t sent your partner request in yet (via the hand-in server, using the process described below), this is your last chance. I’ll be assigning partners this evening, so if you have a preference, make sure you do it by 6 PM today (Sunday).

New Partners, Grade Retrieval, and Lecture Code

Fri, 05 Feb 2010 00:42:54 -0500

I hope you’ve started working on Problem Set 4 with your current partner. For Problem Set 5, we’re going to assign new partners. If you would like to request a partner and they would like to request you, please submit small Scheme program (doesn’t matter what you put in it, so long as the hand-in server accepts it) to the assignment “partners2” along with your requested partner. For example, if Stevie and Vincent wanted to be partners, then they would write something short, like 5 in a DrScheme buffer, and they would submit it as st-amour.v+strickland.t to the dummy assignment “partners2.” Please do this by noon on Sunday if you have a preference. We will consider your request, but we won’t necessarily honor it.

From now on, we will not be returning your homework to you, because we’ve set up a system to allow you to access homework grades and comments. If you want to see the graders’ comments on your work, you’ll have to look there. Login using the same user name and password that you use for the hand-in server. If you have trouble, contact Stevie—he knows how to fix it.

Finally, here’s the lecture code from Wednesday and Thursday.

PS2 Graded, PS4 Available, and Homework Code

Tue, 02 Feb 2010 02:57:01 -0500

I sent out grades for Problem Set 2 to your husky.neu.edu addresses. If you didn’t get it, please let me know, and we can figure out what went wrong.

Problem Set 4 and Monday’s lecture code are posted.

Problem Set 3 Exercise Correction

Mon, 01 Feb 2010 16:10:16 -0500

I’ve corrected the exercise numbers for Problem 4, which were off by one. It used to say 66, 67, and 68, and now it says 65, 66, and 67. Most of you have done or are doing 65, anyway, because it’s a prerequisite for 67. If you’ve already done 68, we’ll grade it for extra credit.

I’m sorry for the inconvenience.

Lecture Code

Thu, 28 Jan 2010 20:20:36 -0500

Yesterday’s actual lecture code, the full version of the painting program, and today’s lecture code are available.

Please remember that if you failed today’s quiz, you need to appear at Vincent’s office hours tomorrow (Friday), Jesse’s on Monday, or Stevie’s on Tuesday in order to get credit for Problem Set 2. You need to be there at least half an hour before the end of office hours to make sure we’ll have time to work with you; likewise, Monday and Tuesday are likely to be very busy, so if you can, we’d recommend going to Vincent’s tomorrow.

Lecture Code, Homework Submission, and Submission Nagging

Mon, 25 Jan 2010 22:21:54 -0500

Today’s lecture code is available.

Please put all your homework problems are in one file. Some people have been creating a separate file for each problem, but if you submit multiple problems in sequence in different files, only the last one will be retained for grading. You may find that it’s annoying to have multiple calls to big-bang in one file. It’s okay to comment out your big-bangs, provided that each one works when uncommented.

There was some confusion today about what it means to “[c]reate a DrScheme buffer.” The DrScheme buffer is the same thing as what in lecture I’ve called the “definitions window”—it’s the place where you write programs. Even though the book says to create a buffer, just add the problems to the same buffer as your other files.

Finally, I understand that only one pair has attempted to submit their homework so far. Please—I urge you—try submitting your homework tonight or tomorrow morning. I don’t expect it to be done by now, but you need to make sure it works before the last minute, and you’ll be able to resubmit it later again any time before the deadline.

Lecture Code, Partners, and Quizzes

Fri, 22 Jan 2010 15:09:56 -0500

Several important notes:

Yesterday’s lecture code is available.
If your partner has dropped and you need a new one, please let me know ASAP.
Just a reminder: If you failed your lab quiz today, in order to receive credit for Problem Set 1, you need to come to Vincent’s office hours on Friday, Jesse’s on Monday, or Stevie’s on Tuesday. Be prepared to convince us that you’ve learned how to solve problems similar to the quiz problem.
If you didn’t take a lab quiz today and you want to receive credit for Problem Set 1, you should come to office hours. In the future, it will not be possible to make up missed quizzes unless you email the instructor before the beginning of the lab that you are going to miss. If for some reason you need to leave lab early, please let us know at the beginning of lab so that we can give you a quiz before you leave.

Electronic Homework Submission

Thu, 21 Jan 2010 21:48:41 -0500

The homework submission server will stop accepting submissions at or very soon after 11:59 PM on Tuesday. We will not look kindly on homeworks emailed to us because you couldn’t get submission to work—especially if they arrive after the deadline—so there are some things we’d recommend you do now to make sure you can submit without a hitch on Tuesday.

First, we’ve noticed that only a minority of you actually performed test submissions to the lab1 assigment during our lab today. We strongly recommend that you do a test submission to the lab1 assignment using the electronic submission instructions before the weekend. If it doesn’t work, you can contact us or come get help at office hours in time to get it fixed by Tuesday.

Also, please make sure that you know your partner’s homework server ID, because you don’t want to find yourself stuck without it on Tuesday evening. (You don’t need to and shouldn’t know your partner’s password.)

Keep in mind that your last submission as of the time the submission window closes is the one that we will grade. This fact has three important implications:

It’s safe and possibly a good idea to submit an incomplete assignment early, because you can submit over it later when you complete more of it.
If you submit a good version of your code, and then mess something up and resubmit, we most likely won’t be able to retrieve the older, good version for you.
In particular, take a look at the Wikipedia article on race conditions, and consider what you can expect if you and your partner accidentally submit different versions of the homework “simultaneously.”

Finally, if you changed your homework submission server password before this evening, we may have accidentally reset your password to your last four NUID digits. If you have trouble logging in with your changed password, you should try the original four digit password. (Sorry.)

Lecture Notes from Wednesday

Thu, 21 Jan 2010 00:21:15 -0500

As promised, here’s the source code from today’s lecture.

Problem Set 2

Wed, 20 Jan 2010 03:38:35 -0500

Problem Set 2 is posted.

Major Reading List Change!

Fri, 15 Jan 2010 01:27:14 -0500

Hello all. I’ve made a significant change to the reading list for the next couple of weeks, starting this morning (Friday). Rather than read from the main textbook, I’ve assigned reading from a new edition, How to Design Programs, Second Edition. HtDP/2e is a work in progress, but many of the changes are based on experience teaching this course over the past few years, and I think you would benefit from reading from this new version.

Please note: The sections in HtDP/2e do not align with sections in your printed textbook and the online version at htdp.org, so please be sure to read from the second edition as linked from the syllabus.

(If you’re behind in the reading or if you are struggling, I suggest that you catch up by reading the Prologue to HtDP/2e.)

Partners Are Not for Problem Set 1

Fri, 15 Jan 2010 01:26:22 -0500

Although we chose partners today in lab, these partners are for Problem Set 2, not Problem Set 1. Please do Problem Set 1 on your own, not with your partner.

For Those of You without Hard-Copy Textbooks

Thu, 14 Jan 2010 01:49:28 -0500

(Note: Updated Fri, 15 Jan 2010 01:37:23 -0500 to mention HtDP/2e.)

It has come to my attention that the bookstore has run out of our textbook, HtDP. Fortunately, for the next few weeks, the reading is from HtDP/2e, which is only available on the web. (Please see the syllabus for the daily reading schedule.)

In two weeks, however, we’ll continue reading from HtDP, first edition. I strongly recommend getting the book in printed form by then. It’s available from Powell’s and Amazon.

Why Doesn’t “rectangle” Work?

Wed, 13 Jan 2010 18:20:03 -0500

Some of you have had a problem creating images in DrScheme. Perhaps you typed something like

    (rectangle 10 10 "solid" "green")

and DrScheme complained: “reference to an identifier before its definition: rectangle.” There’s nothing wrong with that Scheme expression, but you need to tell DrScheme ahead of time that you want to work with images (and eventually, animations), by loading the universe.ss “teachpack.” You can do this by going to the Language>Add Teachpack... menu and selecting universe.ss at the bottom of the list.

Whenever you run a program in DrScheme (by clicking the “Run” button, or pressing cmd-t or ctrl-t), it tells you which teachpacks you have loaded. Mine, for example, says:

     Welcome to DrScheme, version 4.2.3 [3m].
     Language: Beginning Student custom.
     Teachpack: universe.ss.

Yours should say something similar.

Problem Set 1

Tue, 12 Jan 2010 22:35:21 -0500

Problem Set 1 is posted.

CCIS Accounts

Mon, 11 Jan 2010 18:07:00 -0500

I promised in class to provide this link to the CCIS account request form. Fill this out, follow the instructions, and drop it off in the slot outside 310 WVH. I strongly recommend that you do this as soon as possible—if you turn it in by tomorrow (Tuesday), you may have an account in time for lab on Thursday.

Note that this is not the same as your myneu/husky.neu account, so even if you already have one of those accounts, you’ll need to get one of these as well.

Welcome!

Mon, 11 Jan 2010 00:31:18 -0500

Welcome to CS2500! Please check back here often for updates, or subscribe to the RSS feed.