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Friday, December 11th, 2009

The End

This is the end of Bootcamp. You struggled with the material, you lost sleep over problem sets, you coped with a random partner, and you tried to justify your design in front of harsh critics. You survived and, hopefully, you learned something. Indeed, it is my sincere hope that you will remember this time as a harsh but productive immersion into techniques that can help you in many situations. I hope you do, and so do we all from the Bootcamp staff. Good luck with the rest of the MS program and your co-ops.

The rest of the course works like this. Sometime over the weekend you will receive your list of grades in your email. If you find that any of these grades are wrong, please send email to Stephen Chang, who will discuss change requests with the rest of the staff as appropriate. By Tuesday, we will sit down and make up final grades (anonymously) and upload them into the registrar's database by the end of the week.


Friday, December 11th, 2009

Just in case you wish to remember the 10 things you could have learned, I have put the lecture notes from this last week on-line.

In addition, you can find two distinct solutions for problem 12-1 on line:

  • one that is squeezed into the abstraction schema for itemized data definitions (see lecture 12)
  • another one that creates a wider hierarchy and makes intelligent use of abstract classes.

  • Monday, December 7th, 2009

    Tomorrow (Tuesday, 8 Dec 2009), Prof. Felleisen won't have office hours.

    Also tomorrow, only the 3:30-5:30 drill club will take place. The second drill club (5:30-7:30) is canceled.


    Monday, December 7th, 2009

    A student asks
    "Assignment 12 asks us to convert the solution into complete class-oriented solution. Does this imply that we have to implement the (listof X) also as a class?"
    The answer is no. Just replace the global main function from problem set 11 with a call to the expression
    (send (new sis%) go)

    Saturday, December 5th, 2009

    Here is one more comment from the panel. Suppose you need a method that switches a traffic light from one color to another:
    (define traffic% 
     (class object% 
        ...
        ;; String -> Void 
        ;; purpose and effect: change current-state to s
        (define/public (switch-to s) ...)
        ...)
    
    The use of built-in data definition String is, of course, wrong here. You must supply a data definition that restricts the input to switch-to appropriately:
    
    ;; A TC is one of: 
    ;; -- "red"
    ;; -- "green" 
    ;; -- "orange"
    ;; -- "blue"
    
    (define traffic% 
     (class object% 
        ...
        ;; TC -> Void 
        ;; purpose and effect: change current-state to s
        (define/public (switch-to s) ...)
        ...)
    
    Otherwise a future reader will not know which strings are legitimate inputs to switch-to and which ones aren't.

    Friday, December 4th, 2009

    Here are the key insights from this week's code walks:
    1. You must respect the design recipe, even though we have moved on to classes (e.g., data definitions as classes need interpretations; examples and tests are designed before methods; random methods need different kind of testing).
    2. You must formulate two kinds of tests for imperative methods: concerning things that change and concerning things that must remain the same. See blog post from last week.
    3. You must allocate functionality appropriately. For example, when you discuss a tank firing shots, you should immediately imagine a function with this kind contract:
      ;; Tank -> Shot
      And this kind of contract tells you to which class the method belongs. If you instead add a method to the "state of the world" class that uses selectors/getters, you clearly missed the point of the course, which tells you to organize your data around problem structures and to design your functions around these data definitions.
    Finally, you must implement criticisms of your code from the panels. If you don't, we know that you failed in another key aspect, namely, the goal of learning to communicate (which includes listening) about code.

    You have one more chance to demonstrate that you can explain code and listen to criticisms of your code.


    Wednesday, December 2nd, 2009

    Problem set 12 had accidentally switched the order of problems. It is fixed now. Sorry for any inconveniences.

    Tuesday, December 1st, 2009

    Just to clarify, you are welcome to use local for computing local variable bindings, e.g.,

    (define/public (distance x1 y1)
      (local ((define xdelta (- x1 x))
              (define ydelta (- y1 y)))
       (sqrt (+ (* xdelta xdelta) (* ydelta ydelta)))))
    
    in my lecture notes.

    In case you need to do so, you may initialize super-variables as follows:

    
    (define a%
     (class object% 
       (init-field x)
       (super-new)))
    
    (define b%
     (class object% 
       (init-field y)
       (super-new [x (some-function y)])))
    
    This is perfectly legitimate.


    Tuesday, December 1st, 2009

    The lecture notes from Monday night are now available on-line.

    When you design object-oriented programs in the Module language, do not use local to define functions. Even if you succeed to process objects in such functions, these definitions are unjustifiable and will therefore result in huge point losses during code walks. -- You may of course use lambda to create functions for processing lists.

    When you develop examples/tests for imperative methods in stateful classes, you must create each test so that it stands on its own. It must not rely on the execution of previous tests and it must not affect subsequent tests. Here is a skeleton example:

    (check-expect (local ((define o (new some-class% ...)))
    		(begin
    		  (send o change-yourself)
    		  (send o reveal-something-about-yourself)))
                  expected-values-possibly-lists)
    
    And don't forget to formulate tests for the same sequence of commands that shows that no unintended properties of the object change. (With lists you could formulate a single test for this, but it is acceptable to use two unit tests instead to separate the concerns.)

    The topic of tail-call optimization was recently discussed by Guy Steele on Sun's Fortress blog. Recall that Steele is the person who developed Scheme and co-specified Java. His latest language, Fortress, is an attempt to create a highly parallel successor to Fortran with modern OO features and lessons learned from decades of language design. Enjoy!


    Monday, November 30th, 2009

    The 12th and last problem set has been released.

    Wednesday, November 25th, 2009

    I have corrected a small typo in problem 10-1.

    Problem set 11 has been released.

    Happy Thanksgiving!


    Tuesday, November 24th, 2009

    Prof. Wand writes: The working version of 10-worm-imp-wand.ss is now up on the examples directory (Lectures/Wand). There were just a few changes after class, which are clearly marked. You should look at these carefully to understand what went wrong and how it was fixed.

    Tuesday, November 24th, 2009

    Christos asked me to respond to some questions from the drill club on the blog. Here we go:
    1. You may continue to assume the existence of built-in data definitions such as Number, String, Boolean, and those from the Universe teachpack (KeyEvent, MouseEvent, etc). If you happen to need sub-collections of those, make a special-purpose data definition and use as before. -- You may even use [Listof X] for a defined X in your code. -- For everything else, you will need a class-base data representation.
    2. You should not need any plain functions for problem set 10, except for local (lambda) functions in case you use a list iterator (e.g., map, fold, etc.). In case you need a novel operations on lists, break the rules. (I can't think of such an operation.)
    3. You may define global constants and global graphical constants. You may also define local fields that are constant, which is preferable.
    4. You must not use any other superclasses than object%. This topic hasn't been covered yet, though we will do so on Monday.
    5. Don't even think of changing code that we provided. So yes, this leaves you with one global function in your program, which we provide.

    Tuesday, November 24th, 2009

    My notes for lecture 10 are on-line in raw form. Read with caution, experiment especially with the list code for Scheme/Java classes. Design an accumulator-version of length and stress-test it, too.

    For problem sets 10 and 11 (to be posted tomorrow), you must use a class-oriented design. Packaging your functional solution in one big and single class isn't it. You will get a 0 for that, even if your functional solution got a perfect grade. Also, don't use other features than those mentioned in the tutorial on Classes (see tab) and the lectures. For example, if you need access to a field, add a selector method to the class.


    Sunday, November 22nd, 2009

    Problem set 10 is a preliminary version of problem set 11. We will neither collect nor code-walk the results.

    Saturday, November 21st, 2009

    While HtDC uses the ProfessorJ programming language(s) to present design concepts in an object-oriented world, you must solve all homework problems in the Module language using its class system and you should solve all drill problems in this language, too. (If you have written acceptable solution in "applicative" ProfessorJ/Java for the drill problems, we may accept you for drill club this week.)

    Friday, November 20th, 2009

    Ms. Raafia found out that I had once again used DrScheme v4.2.3 (svn head) instead of v4.2.1 to prepare the homework assignment. See corrections in 10-2.

    Friday, November 20th, 2009

    Several people have asked about "letter grades". At this point, it is simply too difficult to give you an accurate estimate of your letter grade, especially since the last three assignments carry a relatively heavy "point weight". Recall though the general guideline for grades in this kind of course (briefly discussed in the first lecture): the cut-of for A-level grades is somewhere between 85% and 90%; for B-level grades it is between 70% and 75%; for a C you will need at least 60%. Also keep in mind that we will drop the score that affects your grade most negatively. You may wish to design a program to determine this grade, because it isn't necessarily the lowest score (in absolute numbers). There will be no other discussion of final grades.

    Others have sent inquiries concerning the final schedule. As you can see from university's schedule and previous blog post, there will be 12 (twelve) homework assignments and the last code walks will take place on December 10 and 11.


    Tuesday, November 17th, 2009

    An email exchange from today:
    On Nov 17, 2009, at 4:38 PM, someone wrote:

    Dear prof.,

    The protocol review before the assignment really helped us to get stared with the assignment. I would totally recommend this kind of practice for all the assignments. It gives us the initial view of how to proceed with the assignment in right direction.

    Thank you.
    Here is the reply:
    Thanks but you realize that one goal of this course is to empower you to develop such data representations on your own. In principle, you should learn this at the undergraduate level and we teach this in the first year courses and reinforce it later. If we reviewed all of these definitions you wouldn't appreciate the difficulties and you wouldn't learn to do things on your own.

    Pain is sometimes needed to learn things, and only people who can take pain can learn. -- Matthias

    Tuesday, November 17th, 2009

    Some of you have asked whether paper-and-pencil art is appropriate in lieu of ascii art for the interaction diagram. I must admit that drawing the diagram for the "chat room" assignment in my favorite text editor (Emacs) took me some five to ten minutes and didn't pose any serious problem. So here is the deal:
    You are welcome to bring along a hand-drawn interaction protocol. It will cost you one (1) point out of a total of 40 to 45 points.
    Note though that if we find a violation of the interaction diagram by your code, it will cost you a lot more one point.

    Tuesday, November 17th, 2009

    Last night, I demoed the state feature in universe for monitoring the changes to the state that your client and/or server program experiences. This feature is only available in DrScheme v4.2.2 and up. Since your solution must run in DrScheme v4.2.1, I recommend that you upgrade only if you encounter a mistake that you simply cannot cope with other than using state. If you do upgrade temporarily, you will also have to change calls to error to take one string only. (I use the cutting edge non-released version so that someone exercises everything all the time.)

    Tuesday, November 17th, 2009

    Ms. Raafia discovered another flaw in the docs for the universe teachpack, which was eliminated quite a while back. (We release every two months, and we build the software, including the docs, every night.) It is probably best if you use
    the online pre-release documentation
    Doing so guarantees that you get to see all the fixes and you don't have to guess what's right or wrong. (Typos, like errors, happen; it's critical that you deal with them quickly.)

    Tuesday, November 17th, 2009

    My notes for lecture 9 are on-line in raw form. Read with caution, experiment with gusto. As you will see, I skipped the non-essential 'design2.ss' exercise. It's boxed in the lecture notes. Try it for yourself, then read my solution.

    To fit with the actual assignment schedule, I have swapped the reading assignments for the last two weeks of the lecture schedule. Since nobody has read anything so far anyway, this won't be an imposition.


    Monday, November 16th, 2009

    Ms. Pratibah and Mr. Baturalp discovered a bug in the documentation for the universe teachpack. The text accompanying on-disconnect was wrong. Here is the improved version:
    (on-disconnect dis-expr)
          dis-expr : (-> UniverseState iworld? bundle?)
    tell DrScheme to invoke dis-expr every time a participating world drops its connection to the server. The first argument is the current state of the universe server, while the second argument is the (representation of the) world that got disconnected. The resulting bundle usually includes this second argument in the third field, telling drscheme not to wait for messages from this world anymore.

    Monday, November 16th, 2009

    You are welcome to change your protocol (interaction diagram, message representation, server and client data definition) if you encounter difficulties with the chosen protocol and/or if you realize that a change may improve your design.

    The purpose of the protocol review was to ensure that you got started in the proper direction. If you believe you can benefit from a second review, feel free to check with a TA. It is unnecessary, however, to get the changes approved.


    Saturday, November 14th, 2009

    Your solution for homework 9 should be a single file, placed into the appropriate directory and named accordingly. You should organize your file like this:
    1. section 1 (labeled "protocol") should contain the interactions diagram in ascii art, plus the data definitions for your server-to-client and client-to-server messages;
    2. section 2 (labeled "server") should contain all definitions for the server code, including a function for starting up the server; and
    3. section 3 (labeled "client") should contain all definitions for the client code, including a function for starting up the client.
    Use 'large letters' to label the sections so that we can use the contour view to navigate the solution. Use at least two instances of drscheme to run the program after you have completed the design. (By now you should know that this sentence means "tested without access to the network".) One drscheme runs the server code from the above file, the others run client codes. For fun, you may also consider running the program across the NEU/CCIS network or a network in your apartment.

    Friday, November 13th, 2009

    See revised problem statement for 9.1.

    A solution for problem 8.2 is now available, and we urge you to study it carefully.

    On recursion: during the last lecture, someone stated that a program was slow because it was recursive. In response I gave you a "lecture" on the lack of basic knowledge on the connection between proper program design and the implementation of function calls. Just in case it isn't clear, this lecture was directed at your undergraduate programs in computer science not at you personally.

    As you should know by now, recursion in functions exists because the data definition is self-referential or because you had an algorithm idea (generative recursion). Since this connection cannot possibly disappear if we wish to design systematically, you need an explanation of recursive function calls. You already know what to tell a recruiter who asks why you would want to use recursion.

    In order to provide you with a proper understanding of this topic, we will insert two short lectures on the nature of function calls and recursion. These lectures should help you overcome the wide-spread preconception that "recursion is slow". They will also equip you with the knowledge to argue with recruiters, just in case they don't know their basic cs history either.


    Wednesday, November 11th, 2009

    FAQ 8-2: All external urls are missing urls because "the creator of a site doesn't have control over the rest of the Web". Do keep in mind that this could be considered an ambiguity and any non-trivial resolution would be considered perfectly correct.

    Messrs. Shah and Mehta requested a new feature for more-io.ss--stripping unnecessary white space from href specifications--and I have added it. This will make your program a bit more useful, but it won't affect code walks of course.


    Tuesday, November 10th, 2009

    Armin Galliker discovered an error in the more-io teachpack. Specifically the function url-html-neighbors did not analyze the entirety of ill-formatted (non-XHTML) HTML pages. I have released a new version of the teachpack.

    Naturally, the error in the teachpack cannot affect your program design. First, you are testing it without access to the web, and Mr. Galliker's discovery is perfect proof of why you wish to do so. Second, the revised teachpack simply delivers longer lists of URIs on some occasions. This does not affect the correctness of your code nor its design.


    Tuesday, November 10th, 2009

    Problem set 9 requires the design of a protocol, which consists of an interactions diagram plus data definitions for message exchanges, server state, and client (world) state. You must have a TA check your paper-and-pencil for problem 9-1 by Thursday November 12, 4pm. Bring the "blessed" protocol to your code walk of problem 9-1. If you proceed without a the blessing of a TA, we will impose a 20% penalty on your code walk.

    Monday, November 9th, 2009

    I have made two minor corrections to problem 8-2. They are marked up.

    Sunday, November 8th, 2009

    As several of you have noticed, the example in problem 8-2 was flawed. I have fixed it. Never mind, it was correct the first time around!

    Also, when you are looking for a closed site, specify the site not its index file. That is, use "http:foo.com/bar/" not "http:foo.com/bar/index.html" as the starting point.


    Saturday, November 7th, 2009

    As several of you have noticed, the geo-code function may produce more than one result. My response is that your program may take the first, the last, or all of them. Indeed, you may even wish to let the user of the code (as opposed to its designer) choose what to do.

    Christos will run Felix's drill on Monday, and he will code-walk a solution to the n queens problem to reinforce generative recursion.

    Also on Monday, Stephen will post sign-up sheets for the remaining code walks (8, 9, 10, and 11).

    Some of you have inquired about the schedule for the Thanksgiving week. The lectures will take place as normal. You will also receive a problem set that is conceptually due on Wednesday before Thanksgiving. We will not conduct code walks for these solutions, however. Instead, you will receive a supplement to the homework assignment and we will code-walk the combined solution. In other words, if you don't design properly, you will be in trouble over Thanksgiving; if you do design properly, the changes will be straightforward.


    Friday, November 6th, 2009

    Two comments on today's code walks:

    1. A termination argument explains why a generative recursive function (or nest of generative recursive functions) reaches its termination condition for all possible inputs. It is not a description of the termination conditions.
    2. While it is technically true that a structural design is a special case of a generative recursion, we consider it wrong in this course to refer to a structural design as a generative one. Unless you have a clear idea that you are going to use a generative recursive strategy--which immediately means that you should pay attention to termination--try structural design first.
    See the following notes.

    The problem of rendering expressions (a poem of a program of rendering things for the web browser and/or text production) will come up at least two more times this year. I therefore urge you to take the comments from your code walk to heart and to fix it up before you move on. Here are some hints:

    1. Use a structural design, even if the problem statement uses words that make it sound like you should use generative recursion.
    2. Find the tasks in the problem statement. Design functions for those. If they share auxiliary functions, make those global.
    3. We generally recommend that you develop everything globally, including accumulator functions. That helps you develop examples and test cases for all of your functions. Once you have completed the design, re-arrange your program and make things local that deserve to be local (at least all accumulator functions).
    If you do try to respond to the code-walk panels, I also urge you to go to next week's drill club and present your revised solution.

    On Monday, Felix's drill club will re-examine "generative recursion", a topic that many of you need to revisit. He will present an alternative solution to the "n queens" problem and demonstrate with a concrete example how to think about problem generation.


    Friday, November 6th, 2009

    It is time to start reading "How to Design Classes." The book is available from the bookstore (either classified as "CS 2510" or "CS 5010"). If they don't have it, the NEU Repro store (around the corner) should be able to produce additional copies. -- While we will not follow the book per se and instead use the full PLT language with classes, the principles of the book apply. Also, seeing the ideas in PLT and Java syntax will be beneficial for you.

    There will be class during Thanksgiving week and there will be a problem set (part 1 of problem set 10). But, there will not be code walks for this part of the problem set.


    Wednesday, November 4th, 2009

    Problem set 9 is released. I also clarified a point in problem set 7.

    Tuesday, November 3rd, 2009

    I posted a small (obvious) fix to problem 7-2.

    Tuesday, November 3rd, 2009

    This time around I have posted lecture notes on:

    1. the first part of last night's lecture
    2. the third part of last night's lecture

    In addition, I have posted my accumulator solution and my direct solution to the "foomble depth" problem. I consider the latter part extremely challenging and I personally wrote it in full Scheme due to a lack of time to write it in ISL with weaker tools. -- For your information, the problem is known in programming languages and compilers courses as "the static distance" or the "de Bruijn index" problem.


    Monday, November 2nd, 2009

    Drill problem 31.3.1 is messed up due to a change to drscheme that happened a couple of years after we released the book but before the latest version of the book was released to the web. Specifically, drscheme now understands all real numbers (and complex) as exact numbers not as floating points (like in other languages).

    If you want inexact numbers, your program must compute them (say (sqrt 2)) or you must write them into your program. For this drill, create an inexact coefficient in g-series like this:

    (define (g-series n)
        (cond
          [(zero? n) empty]
          [else (cons (expt #i-0.99 n) (g-series (sub1 n)))]))
    
      (* 10e15 (apply + (g-series 1000)))
    
      (* 10e15 (apply + (reverse (g-series 1000))))
    
    See what these computations of the "same" sums produce.


    Monday, November 2nd, 2009

    Please send me your solutions to the depth problem for the Foomble language. I have two solutions so far, and the lucky winner(s) get to conduct a public code walk (which as you can imagine, comes with large benefits).

    Monday, November 2nd, 2009

    It is time for the last partner switch. This time you may choose to work with the partner of your choice -- as long as you have not worked with this person before. That is, neither your current partner nor your first partner are candidates for the third round.

    By Wednesday NOON, you and your future partner must hand in a signed joint statement to Stephen Chang. If you do not hand in such a statement at that deadline, we will assign you a random partner. Everyone will get notice (confirmation) about the new partner and pair number assignment by Friday NOON latest.

    Until then, you must continue to work with your current partner, and of course, you must not work with anyone else, including your future partner.


    Sunday, November 1st, 2009

    The original "image-ops.ss" teachpack was developed on a newer drscheme. I have modified it so that it now runs on drscheme v4.2.1, the required version. Please download this new version. (Sun Nov 1 20:30)

    Saturday, October 31st, 2009

    See problem set 7 for small improvements (typos, language). Nothing essential changed.

    I have also release problem set 8.


    Thursday, October 29th, 2009

    For the code walks starting tonight, please bring along an encoding of the following Perthon program in your data representation:
    (
     (def T(X) ret ((? X : (T $$ "a") , (X ++ "b")) ++ "c"))
     ((T $$ "") ++ "d"))
    )
    
    If you have a USB stick, put it on there so that the TAs can quickly test your submission with this example.

    Wednesday, October 28th, 2009

    Someone asked whether it is acceptable to produce a complete solution for the n-queens problem first and to animate it afterward. This is a perfectly acceptable solution (even though it may not be in the original spirit of the question).

    Wednesday, October 28th, 2009

    Problem set 7 is out. I have eliminated one problem to reduce your work load a bit. To compensate, we will inspect your code more closely than we have in the past.

    Tuesday, October 27th, 2009

    Like with ISL, Java, and C, Perthon's syntax comes with names for the various pieces. In
    (def FVariable (PVariable) ret Expression)
    FVariable is the name of the function, PVariable is the function's parameters, and Expression is the function's body.

    Also, you should read

    Second, the only variable names that may occur in the body of the function are the name of the function and the name of the function's parameter
    as follows:
    Second, the only variable names that may occur in the body of the function are the function name in the first position of a function call and the name of the function's parameter.


    Tuesday, October 27th, 2009

    Here is a summary of the in-class 'homework problem from last night's lecture:
    Design the function db, which consumes and produces 'Foomble' expressions. Its purpose is to replace all occurrences of parameters in lambda bodies with names that indicate how far away the binding lambda is. Here are some examples from the information domain:
    1. (lambda (x) x) becomes (lambda (x) zero);
    2. for (lambda (x) (lambda (y) (lambda (z) x))), the function returns (lambda (x) (lambda (y) (lambda (z) three)));
    3. and for (x (lambda (x) (lambda (y) (lambda (z) x)))), the result is (x (lambda (x) (lambda (y) (lambda (z) three))).
    Also recall last night's instructive example. In order to turn numbers into symbols, use
    ;; Number -> Symbol
    ;; convert the given number into a symbol
    (define (number->symbol n)
      (cond
        [(= n 0) 'zero]
        [(= n 1) 'one]
        [(= n 2) 'two]
        [(= n 3) 'three]
        [(= n 4) 'four]
        [else 'etc]))
    and don't nest your parameters deeper than five levels. (A real compiler pass uses a parameterized data description and replaces symbols with natural numbers.)
    Send me your solutions before the next lecture. We will code-walk some in public.

    Saturday, October 24th, 2009

    Felix would like you to know:

    1. The descriptions provided (for Perthon's Program, Definition, Expression, Constant, Variable) are *not* Student Language data definitions.
    2. Corollary of above: the first task *cannot* be the (trivial) act of cut-and-pasting the provided descriptions of Perthon's Program, Definition, Expression, Constant, Variable. Something more significant is required.
    If you believe Felix is wrong, present a justification to Professors Wand and/or Felleisen in person, and we may just let you work with the given definitions.

    Someone asked "Is it allowed to use Vectors in Problem 2?". The answer is:

    Yes, but only immutable vectors, for which you may create a teachpack called vectors-for-isl.ss, which you may then check into SVN. The required language for this problem is Intermediate Student Language with Lambda.


    Friday, October 23rd, 2009

    Here are comments in response to the code walks for week 5:
    1. In the past we have repeatedly insisted on two points, which appear to be in contradiction to each other. On one hand, we have said that data definitions should describe sets of values. On the other hand, we have said that functions are first-class values, just like any other function. Put together, the two ideas suggest that a valid data definition may just enumerate a bunch of functions.

      This is wrong, however. You should only use clauses in data definitions for which you can formulate conditions from (constant-time) predicates. Since it is impossible to compute whether two functions are equal or not (in ISL+ and all other full-fledged programming languages), your data definitions may not enumerate function values. Instead read the book's chapter on abstraction and learn to use the -> data collection constructor with which you can describe function spaces.

      In addition, it is also a bad idea to enumerate specific functions from a design perspective. Just recall our discovery of foldr. We abstracted from sum and product. If we had used the contract "the argument must be either + or *", it would then be impossible to use foldr with any other arguments than those two. Now that you have seen numerous uses of fold, you should appreciate why the proper way to abstract is to use function spaces.

    2. We deducted points from missing attributions of code to previous partnerships. While this requirement has always been marked up in red in problem set 5, you won't find such nice warning labels in the real world. Instead, you will be fired if you use code from somewhere else and don't inform your manager; if you are running your own company and do something like this, you will be sued and that is even more costly.

    3. Also, last week's blogged solution explicitly stated that you must not abstract out recursive or cross-function calls. Some of you did so anyway for the X-expression problems. Don't.

    4. We saw many misuses of local for mutually recursive nests of functions. Here is the proper pattern:

       
         (define (main-f x-changing0 x-always-same)
           (local ((define (lcl-f x-changing)
                       ... x-always-same ...
                       ... (lcl-ggg ... x-changing ...) ...)
                   (define (lcl-ggg x-changing)
                       ... x-always-same ...
                       ... (lcl-ggg ... x-changing ...) ...
                       ... (lcl-ggg ... x-changing ...) ...))
             (lclf x-changing0)))
       
      
      Note that main-f is not called from within the local nest of functions. Why? For design reasons, it would be impossible to re-use the constant arguments (the ones that don't change) without always passing it around. You can thus clarify to any reader that x-always-same really remains the same throughout the computation. For performance reasons, you need to understand that every call to main-f re-creates all these localized functions. This costs time and money. Although the primary focus in this course is on proper design and the justification of design, you must always develop a sense for the cost of your chosen language and you must factor this cost into your design as appropriate. See the book's intermezzo on local for details.

    5. No program---especially world programs---should be run from the Definitions Window. You are to write a main function and apply it in the Interactions window to run the program. In the future, we will deduct points if you run programs from the Definitions Window.

    6. Attend drill cub. Use the resources that we offer. Many people have made the claim that they don't have the time to do the drill problems because they are spending so much time on the problem sets. Based 20 years of teaching experience, be advised that the opposite is true. You are spending so much time on homework problems because you don't solve the drill problems.

    You may have noticed that the base score differs from week to week. Over the next few weeks, the score will gradually increase. The increases reflect the increased complexity of the problem sets as well as the idea that we reward those students who can demonstrate that they learned their lessons from previous code walks.

    Saturday, October 17th, 2009

    Correction on the report from code walks: The reviewers report that many of you use undefined terms in contracts, especially "List". They have asked for permission and have received it to deduct 10 points for the meaningless use of "List" and similar terms.

    On Monday afternoon we will post a sign-up sheet for code walk slots for the new pairs. Please sign up by Tuesday afternoon.


    Friday, October 16th, 2009

    Three comments from today's code walks:
    1. We have jointly decided that all of you need exercise in correcting code and presenting corrected code to code walkers. We will release a revised version of homework set 5 this evening still.

    2. The reviewers report that many of you use undefined terms in data definitions, such as "List" or "X". They have asked for permission and have received it to deduct 10 points for the meaningless use of "List" and similar terms.

    3. All of us have observed that you are still not taking notes properly. When Partner A is presenting, Partner B should be seated, with a copy of the code in his or her hand, taking notes on the reviewers' comments as they are made.

      At the end of the session, both partners should be seated, and should take notes on the reviewers' end-of-session comments.

      If you don't take notes, you will walk away from the session and remember nothing of what was said.

      Again, reviewers will deduct points in the future if partners fail to take notes.


    Friday, October 16th, 2009

    See updates to problem set 5 concerning the problem statement and the re-use of code.

    Most importantly, any attempt to work with your old partner is now considered code theft, and we will prosecute it like any other form of theft. For details, see the problem set.


    Thursday, October 15th, 2009

    This night you will receive an email with the name and email address of your new partner. As of Friday 4pm, you will no longer work with your old partner on anything. Instead, you will contact your new partner to arrange a first meeting as soon as possible.

    Homework set 5 is now available. You must work on this homework set with your new partner. The two of you should start by presenting to each other the solutions for problems 4.1, 4.3, and 3.4. You should choose whatever old solution you think is the best starting point. Do not choose the code from the partner with the higher score, unless the score is (near-) perfect. Keep in mind that a score reflects a combination of presentation skills, justified design, and various other aspects. Do use the chance to practice your code walking skills so that both of you understand the code base equally well.

    The new homework set is a relatively light load compared to previous homework sets---if you have a decent solution to the problems. Keep in mind that when you "edit", you must have a good test suite so that you can quickly re-establish that nothing essential changed. If things change unexpectedly, backtrack to the last point that worked (svn is good for that).


    Tuesday, October 13th, 2009

    The staff discussed the needs of the students. We decided to hold drill clubs today (four hours worth!) and not to hold a question and answer session. Please do take advantage of the drill clubs.

    Sunday, October 11th, 2009

    Problem 4.1 now comes with instructions on how to deal with the additional teachpack. Make sure to check in your program from one computer and to check it out on a different computer to ensure that the SVN commit works.

    Also note the small addition of an emphasis to problem 2.


    Saturday, October 10th, 2009

    Concerning problem 4.1: Prof. Wand's class used the name "XElements" instead of "Xexpr". Also see Prof. Wand's lecture notes. Finally, although Prof. Wand's class did not cover the entire refinement chain of XML representations, the material -- together with the book's file system examples -- suffice for solving this problem.

    Friday, October 9th, 2009

    I have edited two of the problems for problem set 4.

    Since the rule about testing auxiliary functions was obviously misunderstood, you must supply tests for all functions.

    From now on, Christos Dimoulas will hold drill-club hours on Tuesdays from 3:30 to 5:30pm, followed by Stephen Chang's drill club from 5:30 to 7:30pm. They will both use room WVH 166.

    We know that Systems will have a make-up lecture on Thursday. If you are in Systems and you have a conflict with your code walk appointment, send email to Stephen Chang by Tuesday NOON.

    Solutions for today's code walk problems (3.2 and 3.3) are on-line again. Do not count on getting solutions for every week.


    Thursday, October 8th, 2009

    Friday morning's code walks will take place in WVH 166 and the upstairs computer lab. The TAs will post a schedule at both places and will manage the distribution of pairs. Watch and listen for announcements.

    Tuesday, October 6th, 2009

    Due to ``copy and paste'' -- something that we teach you not to do -- the syllabus was messed up. In particular, it mistakenly specified a summary session for this week when we really planned on covering Part IV of HtDP. I have fixed and released a new syllabus.

    Also in response to some questions, I have clarified problem set 3. The additions are type set in red so that you can easily spot them.


    Monday, October 5th, 2009

    We have created a second drill club. Stephen will run the drill club in WVH 166 in lieu of his office hours.

    Also, for some reason, a flawed version of homework set 3 made it to the web server. Please make sure to read the released version from Sunday or later.


    Friday, October 2nd, 2009

    The solution to problem 2.2 is now available. Please download it, study it, and experiment with the code.

    Friday, October 2nd, 2009

    Office hours: As of this week, you may no longer ask the TAs any direct questions about the homework problems. If you need clarification, send email to the staff mailing list (see blog); we promise prompt responses throughout the week. You will not get any answers about code that you wrote.

    Drill club II: Also as of this coming week, Stephen's office hours on Tuesday will be turned into a second drill club. All drill problems and all homework problems from weeks past are legitimate topics for the drill clubs. No questions concerning current or future homework will be answered.

    Christos's Wednesday office hours will serve for last minute questions concerning general topics (lectures, functions in BSL or ISL, drscheme questions, svn questions). He will not answer any questions concerning the homework problems per se.


    Wednesday, September 30th, 2009

    There is no need for a new sign-up sheet. The schedule remains the same while you are with the same partner.

    Wednesday, September 30th, 2009

    Professor Wand has put up the examples for his section in the usual place (see tab). The folder has been reorganized a little, so it no longer has a nice landing page, but it will be easier for you to find and download the examples.

    Wednesday, September 30th, 2009

    Last night's lecture received the following hint concerning Problem 2.4:
    I take it that what was meant was to replace (make-editor String String) by (make-editor LOS1 LOS1) where LOS is a list of 1Strings (1-character strings).
    We wish to ensure that everyone is aware of this hint before the deadline.

    Tuesday, September 29th, 2009

    Today's office hours repeatedly brought up three questions:
    1. Q: "where should we write down the answer to the questions which is been asked in the problem set 2?" A: Write them down as comments in the solution file for the corresponding question.
    2. Q: What is non-standard about the conditions in question 2.1? A: Let's try again:
      "The design recipe demands the use of the same predicate in both cond clauses for the main function. Why? How could you simplify the design?"
    3. Q: Should I use a list of two strings for problem 2.4? A: Of course not! That's totally silly. Think about the string operations you had to design for problem 1.4 and how much easier it is to define these operations using lists (of what?).

    Tuesday, September 29th, 2009

    Prof. Wand sent us the following recommendation:
    Bring paper and a writing implement to the code review. During the head panelist's response you should sit down, remain quiet and take notes. If you do not bring paper and writing implement to the review, you will have points taken off your score.
    We all full-heartedly agree with this statement.

    Monday, September 28th, 2009

    Remember to bring a print-out of today's drill problems for drill club. In addition, you should either email your solutions to Felix (pnkfelix at ccs.neu.edu) or bring them along on a memory stick. Today's password is "heaven".

    On a different note: the course now has its own mailing list, which should make it easier to get responses than individual emails:

    cs5010staff@ccs.neu.edu
    The mailing list includes both instructors and the graduate TAs listed on the course web pages.


    Friday, September 25th, 2009

    The head panelists requested that for problem set 2 you provide templates for all functions via comments:

    #| TEMPLATE FOR FUNCTIONS THAT PROCESS elements from DD:  
    
    (define (f an-dd) 
      (cond 
        [(alternative1? an-dd) ... (selector-1-1 an-dd) ...]
        [(alternative2? an-dd) ... (selector-2-1 an-dd) ...
                               ... (selector-2-2 an-dd) ...]
        ...))
    |#
    
    If you need one and the same template for several functions, writing it down once suffices. Indeed, writing it down several times shows that you do not understand the nature of templates.

    Some comments on your code walk performance:

    1. Just a reminder that we do not grade on a curve. The grades are assigned on an absolute scale.
    2. Almost half of the class received 10 or fewer points out of 20. This score corresponds to a failing grade. That's the bad news.
    3. The good news is that the worst code walk doesn't count against your final grade and, based on our experience, that most of you will learn quickly and improve. To improve, however, means you must sit down and study (!= read) the materials that we provide.
    4. The use of "C style braces/parentheses" issue upset one panel so much that they deducted points. I have requested that these points are returned to you. But, I have amended the style sheet and you must use proper parenthesis style or face deductions in the future.

    Solutions for problem 1/2 and problem 1/3 are now available. Study them well.

    I have also put the grading guidelines for problem 1 on line.


    Friday, September 25th, 2009

    See the web page on code reviews for a general on what we look for in your presentations and how we evaluate your 'package.'

    In addition, please understand that the code review functions according to the following pattern:

    1. The panelists check out your solutions from svn (saved at midnight on the preceding Wednesday), check whether your svn arrangements satisfy the required protocol, run a solution, and check some basic stylistic properties.
    2. Each of you gets around 10 minutes to present a program to the panel. During this time, we will ask clarifying questions, 'pointed' questions (hints that your code and/or your presentation of the code is lacking), and questions to direct your presentations.
    3. The remaining 10 minutes belong to the head panelist. He will diagnose each of your code presentations (including the code) and you must listen and remain quiet so that you hear what went wrong. Ideally you should take notes. Discuss the diagnosis after you leave the room.
    If you have questions concerning the diagnosis or if you do not understand how to eliminate the weaknesses that the panel diagnosed, see the teaching assistants and the instructors during office hours.

    On an unrelated note, see the Hollywood principle to get an idea why we introduce you to world programming first.


    Tuesday, September 22nd, 2009

    Office hours postponed!

    Felleisen: today at 3:00-5:00pm instead of the regular times.

    The password is "Faust!" and the code for last night's lecture will appear here soon.


    Monday, September 21st, 2009

    Today's password: "good bye world"

    Now that you have experienced pair programming for 20 minutes, you should read up on it and how it benefits companies and academia alike. The assignments page now has an additional tab, which explains pair programming and which points to a widely popular article on the technique. We urge you to read it, especially if you have doubts, or if you are tempted to split the projects after all and to just do things as you have always done them---all by yourself.

    Hot of the press: an article in yesterday's NYT on pair programming.

    The last day of classes is December 12, as defined by the registrar's calendar.


    Friday, September 18th, 2009

    We have now specified how each and every SVN homework submission must be organized. See the Assignments tab on the left.

    The "last day of classes" is a technical term in US colleges; see NEU's on-line calendar and find out what the last day of classes for this year's fall semester is.


    Friday, September 18th, 2009

    Stephen Chang has prepared a detailed svn demo for your off-line perusal. If your lab was a bit fast and you have never seen anything like svn (trac, csv, etc.), we urge you to spend 15 minutes going through this worksheet carefully.

    Remember: Use

    svn ci -m"problem N.M"
    every time you end a session.


    Thursday, September 17th, 2009

    Today's password: "hello world"

    Once again, today's (and tomorrow's) lab is on-line, and you should read it in preparation of your lab sessions.

    The current version of HtDP/2e refers to a function called animate. Like all other functions, it is hyper-linked to its (draft) documentation. By following the hyper-link, you will see that it is just a new name for the function run-simulation. So use the latter instead of the former if you wish to run the programs in the Prologue.

    Our current plan is to make the last day of classes the last day of Bootcamp. See the campus calendar for details.


    Wednesday, September 16th, 2009

    Professor Wand's lecture notes are now available from his web page. See new tab on the left.

    Wednesday, September 16th, 2009

    One of your co-students writes:
    There's a neat spider service called Page2RSS that periodically scans a given URL for updates and delivers them as an RSS feed. I was able to use it to check the CS5010 class blog. Hopefully it will work well.
  • Page2RSS site: http://page2rss.com/
  • CS5010 class blog feed: http://page2rss.com/rss/e6be6b5b36385e5ec4034e13ad4acc7e
  • If you find this service useful, fine by us. No warranties.

    Tuesday, September 15th, 2009

    Lab 1 is now available. You can start thinking about it early.

    Some important points concerning the course, the labs, and the web pages:
    • The labs will take place in WVH 212 this Thursday and Friday.
    • Remember to get a CCIS systems account before you come to lab. See FAQ.
    • The web pages are still evolving, while we are eliminating typos and adding a few details here and there. Check back often.

    Wednesday, September 9th, 2009

    Welcome to Bootcamp.

    It is time to get started, and this means for you that you must begin to study How to Design Programs/2nd edition. Notice that we didn't use 'read' but 'study' in the preceding sentence. To study a text book means to work through the examples (with drscheme in this case) and to solve some of the exercises to test your knowledge. Any other interaction with a text book is a waste of time.


    last updated on Fri Dec 11 17:00:21 EST 2009generated with PLT Scheme