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  • What kind of knowledge do you need to invent a new programming language?

    - by systempuntoout
    I just finished to read "Coders at works", a brilliant book by Peter Seibel with 15 interviews to some of the most interesting computer programmers alive today. Well, many of the interviewees have (co)invented\implemented a new programming language. Some examples: Joe Armstrong: Inventor of Erlang L. Peter Deutsch: implementer of Smalltalk-80 Brendan Eich: Inventor of JavaScript Dan Ingalls: Smalltalk implementor and designer Simon Peyton Jones: Coinventor of Haskell Guy Steele: Coinventor of Scheme Is out of any doubt that their minds have something special and unreachable, and i'm not crazy to think i will ever able to create a new language; i'm just interested in this topic. So, imagine a funny\grotesque scenario where your crazy boss one day will come to your desk to say "i want a new programming language with my name on it..take the time you need and do it", which is the right approach to studying this fascinating\intimidating\magic topic? What kind of knowledge do you need to model, design and implement a brand new programming language?

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  • The woes of (sometimes) storing "date only" in datetimes

    - by Heinzi
    We have two fields from and to (of type datetime), where the user can store the begin time and the end time of a business trip, e.g.: From: 2010-04-14 09:00 To: 2010-04-16 16:30 So, the duration of the trip is 2 days and 7.5 hours. Often, the exact times are not known in advance, so the user enters the dates without a time: From: 2010-04-14 To: 2010-04-16 Internally, this is stored as 2010-04-14 00:00 and 2010-04-16 00:00, since that's what most modern class libraries (e.g. .net) and databases (e.g. SQL Server) do when you store a "date only" in a datetime structure. Usually, this makes perfect sense. However, when entering 2010-04-16 as the to date, the user clearly did not mean 2010-04-16 00:00. Instead, the user meant 2010-04-16 24:00, i.e., calculating the duration of the trip should output 3 days, not 2 days. I can think of a few (more or less ugly) workarounds for this problem (add "23:59" in the UI layer of the to field if the user did not enter a time component; add a special "dates are full days" Boolean field; store "2010-04-17 00:00" in the DB but display "2010-04-16 24:00" to the user if the time component is "00:00"; ...), all having advantages and disadvantages. Since I assume that this is a fairly common problem, I was wondering: Is there a "standard" best-practice way of solving it? If there isn't, have you experienced a similar requirement, how did you solve it and what were the pros/cons of that solution?

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  • Bubble Breaker Game Solver better than greedy?

    - by Gregory
    For a mental exercise I decided to try and solve the bubble breaker game found on many cell phones as well as an example here:Bubble Break Game The random (N,M,C) board consists N rows x M columns with C colors The goal is to get the highest score by picking the sequence of bubble groups that ultimately leads to the highest score A bubble group is 2 or more bubbles of the same color that are adjacent to each other in either x or y direction. Diagonals do not count When a group is picked, the bubbles disappear, any holes are filled with bubbles from above first, ie shift down, then any holes are filled by shifting right A bubble group score = n * (n - 1) where n is the number of bubbles in the bubble group The first algorithm is a simple exhaustive recursive algorithm which explores going through the board row by row and column by column picking bubble groups. Once the bubble group is picked, we create a new board and try to solve that board, recursively descending down Some of the ideas I am using include normalized memoization. Once a board is solved we store the board and the best score in a memoization table. I create a prototype in python which shows a (2,15,5) board takes 8859 boards to solve in about 3 seconds. A (3,15,5) board takes 12,384,726 boards in 50 minutes on a server. The solver rate is ~3k-4k boards/sec and gradually decreases as the memoization search takes longer. Memoization table grows to 5,692,482 boards, and hits 6,713,566 times. What other approaches could yield high scores besides the exhaustive search? I don't seen any obvious way to divide and conquer. But trending towards larger and larger bubbles groups seems to be one approach Thanks to David Locke for posting the paper link which talks above a window solver which uses a constant-depth lookahead heuristic.

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  • Using Traveling Salesman Solver to Decide Hamiltonian Path

    - by Firas Assaad
    This is for a project where I'm asked to implement a heuristic for the traveling salesman optimization problem and also the Hamiltonian path or cycle decision problem. I don't need help with the implementation itself, but have a question on the direction I'm going in. I already have a TSP heuristic based on a genetic algorithm: it assumes a complete graph, starts with a set of random solutions as a population, and works to improve the population for a number of generations. Can I also use it to solve the Hamiltonian path or cycle problems? Instead of optimizing to get the shortest path, I just want to check if there is a path. Now any complete graph will have a Hamiltonian path in it, so the TSP heuristic would have to be extended to any graph. This could be done by setting the edges to some infinity value if there is no path between two cities, and returning the first path that is a valid Hamiltonian path. Is that the right way to approach it? Or should I use a different heuristic for Hamiltonian path? My main concern is whether it's a viable approach since I can be somewhat sure that TSP optimization works (because you start with solutions and improve them) but not if a Hamiltonian path decider would find any path in a fixed number of generations. I assume the best approach would be to test it myself, but I'm constrained by time and thought I'd ask before going down this route... (I could find a different heuristic for Hamiltonian path instead)

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  • Generating all unique combinations for "drive ya nuts" puzzle

    - by Yuval A
    A while back I wrote a simple python program to brute-force the single solution for the drive ya nuts puzzle. The puzzle consists of 7 hexagons with the numbers 1-6 on them, and all pieces must be aligned so that each number is adjacent to the same number on the next piece. The puzzle has ~1.4G non-unique possibilities: you have 7! options to sort the pieces by order (for example, center=0, top=1, continuing in clockwise order...). After you sorted the pieces, you can rotate each piece in 6 ways (each piece is a hexagon), so you get 6**7 possible rotations for a given permutation of the 7 pieces. Totalling: 7!*(6**7)=~1.4G possibilities. The following python code generates these possible solutions: def rotations(p): for i in range(len(p)): yield p[i:] + p[:i] def permutations(l): if len(l)<=1: yield l else: for perm in permutations(l[1:]): for i in range(len(perm)+1): yield perm[:i] + l[0:1] + perm[i:] def constructs(l): for p in permutations(l): for c in product(*(rotations(x) for x in p)): yield c However, note that the puzzle has only ~0.2G unique possible solutions, as you must divide the total number of possibilities by 6 since each possible solution is equivalent to 5 other solutions (simply rotate the entire puzzle by 1/6 a turn). Is there a better way to generate only the unique possibilities for this puzzle?

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  • Turing-Complete language possibilities?

    - by I can't tell you my name.
    In every Turing-Complete language, is it possible to create a working Compiler for itself which first runs on an interpreter written in some other language and then compiles it's own source code? (Bootstrapping) Standards-Compilant C++ compiler which outputs binaries for, e.g.: Windows? Regex Parser and Evaluater? World of Warcraft clone? (Assuming the language gets the necessary API bindings as, for example, OpenGL and the WoW source code is available) (Everything here theoretical) Let's take Brainf*ck as an example language.

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  • How do you mock a Sealed class?

    - by Brett Veenstra
    Mocking sealed classes can be quite a pain. I currently favor an Adapter pattern to handle this, but something about just keeps feels weird. So, What is the best way you mock sealed classes? Java answers are more than welcome. In fact, I would anticipate that the Java community has been dealing with this longer and has a great deal to offer. But here are some of the .NET opinions: Why Duck Typing Matters for C# Develoepers Creating wrappers for sealed and other types for mocking Unit tests for WCF (and Moq)

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  • What happens if two COM classes each without a threading model are implemented in one in-proc COM se

    - by sharptooth
    Consider a situation. I have an in-proc COM server that contains two COM classes. Both classes are marked as "no threading model" in the registry - the "ThreadingModel" value is just absent. Both classes read/write the same set of global variable without any synchronization. As far as I know "no threading model" will enforce COM to disallow concurrent access to the same or different instances of the same class by different threads. Will COM prevent concurrent access to instances of the two abovementioned different classes? Do I need synchronization when accessing the global variables from two different COM classes in this situation?

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  • Heuristic to identify if a series of 4 bytes chunks of data are integers or floats

    - by flint
    What's the best heuristic I can use to identify whether a chunk of X 4-bytes are integers or floats? A human can do this easily, but I wanted to do it programmatically. I realize that since every combination of bits will result in a valid integer and (almost?) all of them will also result in a valid float, there is no way to know for sure. But I still would like to identify the most likely candidate (which will virtually always be correct; or at least, a human can do it). For example, let's take a series of 4-bytes raw data and print them as integers first and then as floats: 1 1.4013e-45 10 1.4013e-44 44 6.16571e-44 5000 7.00649e-42 1024 1.43493e-42 0 0 0 0 -5 -nan 11 1.54143e-44 Obviously they will be integers. Now, another example: 1065353216 1 1084227584 5 1085276160 5.5 1068149391 1.33333 1083179008 4.5 1120403456 100 0 0 -1110651699 -0.1 1195593728 50000 These will obviously be floats. PS: I'm using C++ but you can answer in any language, pseudo code or just in english.

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  • GData for my own API?

    - by Malax
    Hi StackOverflow! Im currently planning to build an API for my service. I want to use GData because it fits the application scheme and there are libraries for many programming languages available. The first question that rose: Am I allowed to do that? I mean, Google put lots of work into the GData specification and have some sort of copyright. Does anyone know anything about this issue or did that before? You could extend the case if you want to specifically mimic an API which uses GData like the YouTube API to have my API 100% compliant. This is not my case, but I was wondering about that too. :-) Thank you for any input, Malax Edit: Note that i want to use it for my own service. So, I am implementing an API using the GData protocol, not using one of the Google APIs.

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  • given two bits in a set of four, fine position of two other bits

    - by aaa
    hello I am working on a simple combinatorics part, and found that I need to recover position of two bits given position of other two bits in 4-bits srring. for example, (0,1) maps to (2,3), (0,2) to (1,3), etc. for a total of six combinations. My solution is to test bits using four nested ternary operators: ab is a four bit string, with two bits set. c = ((((ab & 1) ? (((ab & 2) ? ... ))) : 0) abc = ab | c recover the last bit in the same fashion from abc. can you think of a better way/more clever way? thanks

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  • Code Golf: Quickly Build List of Keywords from Text, Including # of Instances

    - by Jonathan Sampson
    I've already worked out this solution for myself with PHP, but I'm curious how it could be done differently - better even. The two languages I'm primarily interested in are PHP and Javascript, but I'd be interested in seeing how quickly this could be done in any other major language today as well (mostly C#, Java, etc). Return only words with an occurrence greater than X Return only words with a length greater than Y Ignore common terms like "and, is, the, etc" Feel free to strip punctuation prior to processing (ie. "John's" becomes "John") Return results in a collection/array Extra Credit Keep Quoted Statements together, (ie. "They were 'too good to be true' apparently")Where 'too good to be true' would be the actual statement Extra-Extra Credit Can your script determine words that should be kept together based upon their frequency of being found together? This being done without knowing the words beforehand. Example: "The fruit fly is a great thing when it comes to medical research. Much study has been done on the fruit fly in the past, and has lead to many breakthroughs. In the future, the fruit fly will continue to be studied, but our methods may change." Clearly the word here is "fruit fly," which is easy for us to find. Can your search'n'scrape script determine this too? Source text: http://sampsonresume.com/labs/c.txt Answer Format It would be great to see the results of your code, output, in addition to how long the operation lasted.

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  • How to work with this turing machine?

    - by Lazer
    This is a screenshot of the applet LogiCell 1.0, link to which I found here. As the bottom left corner shows, this is doing sum 0+1 and the result is 01b (bottom right hand side). I am not able to link what is displayed to what the inputs ans outputs are. For example in this case - seeing the snapshot, how do you determine that the inputs are 0 and 1 and the output is 01?

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  • Pair programming: How should the pairs be chosen?

    - by Jon Seigel
    This topic has been covered peripherally in bits and pieces in some of the other pair-programming questions, but I want to (a) consolidate this knowledge into a separate question, and, most importantly, (b) go into much more depth on the subject. From the perspective of being an effective manager, how should pairs be arranged for pair programming to maximize both the happiness and productivity of the overall team? Some ideas to get started: Should two people never be paired (because of personalities, for example)? How much overlap in skillsets is needed? How much disconnect in skillsets is too much to overcome? (No two people will overlap 100%, and a disconnect in skills can be very beneficial to both people.) Should everyone pair with everyone else on a fixed/rotating basis? Should certain pairs be arranged to accomplish specific tasks? How important a role does HR play when growing or reorganizing the team?

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  • What technologies should I focus on to work as a developer in Japan?

    - by Atomiton
    I'm thinking of one day moving to Japan and I was wondering if anyone here has any experience working there. I'm curious as to what languages/technology are popular there for web development and software development. I have heard Ruby is/was strong there due to its founder being Japanese. What would you recommend someone focus on if they wanted to work as a developer in Japan? I have heard Microsoft has a strong base in Japan, but my guess is that whatever platform has supported unicode or Shift-JIS the best would be the strongest.

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  • how to better (inambiguaously) use the terms CAPTCHA and various types of interactions?

    - by vgv8
    I am working on survey of state-of-the-art and trends of spam prevention techniques. I observe that non-intrusive, transparent to visitor spam prevention techniques (like context-based filtering or honey traps) are frequently called non-captcha. Is it correct understanding of term CAPTCHA which is "type of challenge-response [ 2 ]test used in computing to ensure that the response is not generated by a compute" [ 1 ] and challenge-response does not seem to imply obligatory human involvement. So, which understanding (definition) of term and classification I'd better to stick with? How would I better call CAPTCHA without direct human interaction in order to avoid ambiguity and confusion of terms understnding? How would I better (succinctly and unambiguously) coin the term for captchas requiring human interaction but without typing into textbox? How would I better (succinctly and unambiguously) coin the terms to mark the difference between human interaction with images (playing, drag&dropping, rearranging, clicking with images) vs. just recognizing them (and then typing into a textbox the answer without interaction with images)? PS. The problem is that recognition of a wiggled word in an image or typing the answer to question is also interaction and when I start to use the terms "interaction", "interactive", "captcha", "protection", "non-captcha", "non-interactive", "static", "dynamic", "visible", "hidden" the terms overlap ambiguously with which another (especailly because the definitions or their actual practice of usage are vague or contradictive). [ 1 ] http://en.wikipedia.org/wiki/CAPTCHA

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  • Looking for examples of "real" uses of continuations

    - by Sébastien RoccaSerra
    I'm trying to grasp the concept of continuations and I found several small teaching examples like this one from the Wikipedia article: (define the-continuation #f) (define (test) (let ((i 0)) ; call/cc calls its first function argument, passing ; a continuation variable representing this point in ; the program as the argument to that function. ; ; In this case, the function argument assigns that ; continuation to the variable the-continuation. ; (call/cc (lambda (k) (set! the-continuation k))) ; ; The next time the-continuation is called, we start here. (set! i (+ i 1)) i)) I understand what this little function does, but I can't see any obvious application of it. While I don't expect to use continuations all over my code anytime soon, I wish I knew a few cases where they can be appropriate. So I'm looking for more explicitely usefull code samples of what continuations can offer me as a programmer. Cheers!

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  • What "already invented" algorithm did you invent?

    - by Guy
    In my question Insert Update stored proc on SQL Server I explained an efficient way of doing an insert/update - perhaps THE most efficient. It's nothing amazing but it's a small algorithm that I came up with in a mini-Eureka moment. Although I had "invented" it by myself and secretly hoped that I was the first to do so I knew that it had probably been around for years but after posting on a couple of lists and not getting confirmation I had never found anything definitive written up about it. So my questions: What software algorithm did you come up with that you thought that you'd invented? Or better yet, did you invent one?

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  • Is it viable and necessary to encrypt bytes?

    - by Shervin
    We have a requirement from customer that if someone gets access to the database, all data that includes personal information should be encrypted, so that when they do select calls, they shouldn't be able to see anything in clear text. Now this isn't any problem for Strings, but what about bytearrays? (that can potentially be quite huge (several 100mb)) When you do a select call, you get gibberish anyways. Is it possible for a hacker to somehow read the bytes and get the sensitive information without knowing how the structure of the object it is mapped against is? Because if that is the case, then I guess we should encrypt those bytes, even if they can potentially be quite huge. (I am guessing adding encryption will make them even bigger)

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  • Any Open Source Pregel like framework for distributed processing of large Graphs?

    - by Akshay Bhat
    Google has described a novel framework for distributed processing on Massive Graphs. http://portal.acm.org/citation.cfm?id=1582716.1582723 I wanted to know if similar to Hadoop (Map-Reduce) are there any open source implementations of this framework? I am actually in process of writing a Pseudo distributed one using python and multiprocessing module and thus wanted to know if someone else has also tried implementing it. Since public information about this framework is extremely scarce. (A link above and a blog post at Google Research)

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  • Is currying just a way to avoid inheritance?

    - by Alex Mcp
    So my understanding of currying (based on SO questions) is that it lets you partially set parameters of a function and return a "truncated" function as a result. If you have a big hairy function takes 10 parameters and looks like function (location, type, gender, jumpShot%, SSN, vegetarian, salary) { //weird stuff } and you want a "subset" function that will let you deal with presets for all but the jumpShot%, shouldn't you just break out a class that inherits from the original function? I suppose what I'm looking for is a use case for this pattern. Thanks!

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