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• Clojure for a lisp illiterate

  - by dbyrne

  I am a lifelong object-oriented programmer. My job is primarily java development, but I have experience in a number of languages. Ruby gave me my first real taste of functional programming. I loved the features Ruby borrowed from the functional paradigm such as closures and continuations. Eventually, I graduated to Scala. This has been a great way to gradually learn to approach non-trivial problems in a functional manner. Now I am interested in Clojure. I know all the sexy features that make it enticing (software transactional memory, macros, etc.), but I just can't get used to "thinking in lisp". I've seen Rich Hickey's screencasts aimed at java programmers, but they are geared towards explaining language features and not approaching real world problems. I am looking for any advice or resources which have made this transition easier for others.

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• Write the longest possible loop.

  - by Abhay

  Hello Group, Recently I was asked this question in a technical discussion. What is the longest possible loop that can be written in a programming language? This loop has to be as long as possible and yet not an infinite loop and should not end-up crashing the program (Recursion etc...) I honestly did not know how to attack this problem, so I asked him if is it practically possible. He said using some computer science concepts, you can arrive at a hypothetical number which may not be practical but nevertheless it will still not be infinite. Anyone here; knows how to analyse / attack this problem. P.S. Choosing some highest limit for a type that can store the highest numerical value is apparently not an answer. Thanks in advance,

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• Is there a way of providing a final transform method when chaining operations (like map reduce) in underscore.js?

  - by latentflip

  (Really strugging to title this question, so if anyone has suggestions feel free.) Say I wanted to do an operation like: take an array [1,2,3] multiply each element by 2 (map): [2,4,6] add the elements together (reduce): 12 multiply the result by 10: 120 I can do this pretty cleanly in underscore using chaining, like so: arr = [1,2,3] map = (el) -> 2*el reduce = (s,n) -> s+n out = (r) -> 10*r reduced = _.chain(arr).map(map).reduce(reduce).value() result = out(reduced) However, it would be even nicer if I could chain the 'out' method too, like this: result = _.chain(arr).map(map).reduce(reduce).out(out).value() Now this would be a fairly simple addition to a library like underscore. But my questions are: Does this 'out' method have a name in functional programming? Does this already exist in underscore (tap comes close, but not quite).

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• Best solution to wait for all ajax callbacks to be executed

  - by glaz666

  Hi! Imagine we have to sources to be requested by ajax. I want to perform some actions when all callbacks are triggered. How this can be done besides this approach: (function($){ var sources = ['http://source1.com', 'http://source2.com'], guard = 0, someHandler = function() { if (guard != sources.length) { return; } //do some actions }; for (var idx in sources) { $.getJSON(sources[idx], function(){ guard++; someHandler(); }) } })(jQuery) What I don't like here is that in this case I can't handle response failing (eg. I can't set timeout for response to come) and overall approach (I suppose there should be a way to use more power of functional programming here) Any ideas? Regards!

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• Tips for measuring the parallelism speed-up in multi-core development.

  - by fnCzar

  I have read many of the good questions and answers around multi-core programming how-tos etc. I am familiar with concurrency, IPC, MPI etc but what I need is advice on how to measure speed-up which will help in making a business case of spending the time to write such code. Please don't answer with "well run it with single-core code then multi-core code and figure out the difference". This is neither a scientific nor a reliable way to measure performance improvement. If you know of tools that will do some of the heavy lifting please mention them. Answers pertaining to methodology will be more fitting but listing tools is ok as well.

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• Can you use #defined values in if statements (In C programs)?

  - by Jordan S

  I am new at C programming. I thought when you type something like #define Const 5000 that the compiler just replaces every instance of Const with 5000 at compile time. Is that wrong? I try doing this in my code and I get a syntax error. Why can't i do this? #define STEPS_PER_REV 12345 ... in some function if(CurrentPosition >= STEPS_PER_REV) { // do some stuff here } The compiler complains about the if statement with a syntax error that gives me no details.

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• How to evaluate text strings provided by sed/grep/whatever?

  - by T.J.

  This is for UNIX shell programming. It have to be supported by multiple UNIX platforms including Solaris, Linux, and AIX. I have this scenario -- I am to read from a text file a string that may or may not contain an environment variable that may or may not be defined. For example: <foo.bar> This error code was found: $(error_code) I have the following code: statement=$(sed -n $1'p' $messagefile) echo $echo_flag $statement $1 = line number supplied to this particular function/script. $messagefile = filename of log file. $echo_flag = "-e" in Linux, otherwise, empty. $(error_code) = 42. Instead of getting this when running: <foo.bar> This error code was found: 42 I still get this: <foo.bar> This error code was found: $(error_code) How exactly do I tell the shell script that the value of statement should be evaluated further beyond what sed have done?

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• client-server application design

  - by nelly

  Hi, i want to create a client-server application using sockets on .net platform and being new to networking programming and i have a dilemma. The client will send data to server often and also the server will notify clients often. What is the best way to design it? should the server keep a thread to communicate with each client until it quits or just the clients send data to the server and it update the clients regularly(few seconds) or none of those? Some help would be great. Thanks guys.

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• Experiences teaching or learning map/reduce/etc before recursion?

  - by Jay

  As far as I can see, the usual (and best in my opinion) order for teaching iterting constructs in functional programming with Scheme is to first teach recursion and maybe later get into things like map, reduce and all SRFI-1 procedures. This is probably, I guess, because with recursion the student has everything that's necessary for iterating (and even re-write all of SRFI-1 if he/she wants to do so). Now I was wondering if the opposite approach has ever been tried: use several procedures from SRFI-1 and only when they are not enough (for example, to approximate a function) use recursion. My guess is that the result would not be good, but I'd like to know about any past experiences with this approach.

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• Javascript: best solution to wait for all ajax callbacks to be executed

  - by glaz666

  Hi! Imagine we have to sources to be requested by ajax. I want to perform some actions when all callbacks are triggered. How this can be done besides this approach: (function($){ var sources = ['http://source1.com', 'http://source2.com'], guard = 0, someHandler = function() { if (guard != sources.length) { return; } //do some actions }; for (var idx in sources) { $.getJSON(sources[idx], function(){ guard++; someHandler(); }) } })(jQuery) What I don't like here is that in this case I can't handle response failing (eg. I can't set timeout for response to come) and overall approach (I suppose there should be a way to use more power of functional programming here) Any ideas? Regards!

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• Does the Internet make us less good programmers? [closed]

  - by stagas

  With all the information and code available nowadays on the Internet has that diminished our capability of remembering or learning stuff just because we know they're available somewhere out there, just a Google away or a StackOverflow question away? For example I find myself visiting php.net quite often to check the syntax of the same functions over and over again, not because my memory sucks, but I don't feel like keeping the information in me, since I know I'll find it again on the net. And about StackOverflow, isn't the process of figuring things out on your own supposed to improve your programming skills? If the answers are all just clicks away, do we actually learn something or just keep a pointer in our heads where to search for it again when we need it? Your thoughts are welcome. Hope it doesn't shut down as subjective or anything, the answers would be really interesting ;)

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• Instantiating Java object with a passed in method

  - by superluminary

  It's been a few years since I've been heavily into Java. Coming back to it I'm seeing this pattern all over the place: ratingBar.setOnRatingBarChangeListener(new OnRatingBarChangeListener() { public void onRatingChanged(RatingBar ratingBar, float rating, boolean fromUser) { // do work } }); This looks more like Functional programming to me. It's a nice pattern but how is it possible to pass a method like this? In the old days a class was a class, and once compiled there was little you could do to it. My questions are: Can anyone let me know what this pattern is called? How can I write a class that can be instantiated in this way. Are there any other useful examples of functional patterns that have made their way into Java? What do I need to Google to read more about this? Thanks.

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• Interesting or unique types encountered?

  - by user318904

  What is the most strange or unique type you have seen in a programming language? I was thinking the other day about a "random variable", ie whenever it is evaluated it yields a random value from some domain. It would require some runtime trickery. Also I bet there can be some interesting mapping of regular expressions into a type system. It does not necessarily have to be a built in or primitive type, but some random class that implements a domain specific type won't really be interesting just unique.

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• Change IP settings using C++

  - by Chris

  How do I change the IP settings of a Windows CE 6 box Programatically via C++? Functions for Windows might also work. I found that I can change the hostname via sethostname but couldn't find how to change IP address settings such as: IP Address DHCP Subnet Gateway DNS1 / DNS2 WINS1 / WINS2 Any advice / pointers would be great. Thanks. P.s. How would you get the box to update to those settings - is a refresh or the programming equivalent of ipconfig /renew required?

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• C/C++ detect network type

  - by Gavimoss

  I need to write a win32 c/c++ application which will be able to determine whether the PC it's running on is connected to one of 2 networks. The first network is the company LAN (which has no internet connection) and the second network is a standalone switch with a single PC connected to it (the PC that the program is running on). I'm pretty new to network programming but so far I have tried testing to see if a network drive which is held on our LAN can be mapped. This works fine if the PC is connected to the LAN, the drive mapping succeeds so so LAN detection is successful. However, if the PC is connected to the switch, this results in a VERY long timeout which is not a suitable as it will delay the program so much as to make it unusable. Does anyone have any alternative suggestions? I'm using c/c++ in VS 6.0

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• Is there any Application Server Frameworks for other languages/platforms than JavaEE and .NET?

  - by Jonas

  I'm a CS student and has rare experience from the enterprise software industry. When I'm reading about enterprise software platforms, I mostly read about these two: Java Enterprise Edition, JavaEE .NET and Windows Communication Foundation By "enterprise software platforms" I mean frameworks and application servers with support for the same characteristics as J2EE and WCF has: [JavaEE] provide functionality to deploy fault-tolerant, distributed, multi-tier Java software, based largely on modular components running on an application server. WCF is designed in accordance with service oriented architecture principles to support distributed computing where services are consumed by consumers. Clients can consume multiple services and services can be consumed by multiple clients. Services are loosely coupled to each other. Is there any alternatives to these two "enterprise software platforms"? Isn't any other programming languages used in a bigger rate for this problem area? I.e Why isn't there any popular application servers for C++/Qt?

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• What was your first home computer?

  - by Adam Tegen

  What was your first home computer? The one that made you "fall in love" with programming. There are 300+ entries, many (most?) of which are duplicates. As with all StackOverflow Poll type Q&As, please make certain your answer is NOT listed already before adding a new answer - searching doesn't always find it (model naming variations, I assume). If it already exists, vote that one up so we see what the most popular answer is, rather than duplicating an existing entry. If you see a duplicate, vote it down so the top entries have only one of each model listed. If you have interesting or additional information to add, use a comment or edit the original entry rather than creating a duplicate.

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• Can JavaScript be overused?

  - by ledhed2222

  Hello stackoverflow, I'm a "long time reader first time poster", glad to start participating in this forum. My experience is with Java, Python, and several audio programming languages; I'm quite new to the big bad web technologies: HTML/CSS/JavaScript. I'm making two personal sites right now and am wondering if I'm relying on JavaScript too much. I'm making a site where all pages have a bit of markup in common--stuff like the nav bar and some sliced background images--so I thought I'd make a pageInit() function to insert the majority of the HTML for me. This way if I make a change later, I just change the script rather than all the pages. I figure if users are paranoid enough to have JavaScript turned off, I'll give them an alert or something. Is this bad practice? Can JavaScript be overused? Thanks in advance.

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• Would Lisp be extremely difficult for a new(ish) programmer to learn?

  - by Rubber Duchy

  I've got a little experience with Python (enough to where I can do if/else/elif and some random number generation), but I've always had a weird fascination with the Lisp languages. I downloaded some scheme source code to look at the syntax but it was pretty much gibberish to me. For a programmer with only a little programming experience like myself, given some good books, websites, and some time, would it be particularly difficult to learn either Common Lisp or Scheme? Which of the two would be easier? How do they compare with Python and C, as far as ease of learning? Thanks

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• So my girlfriend wants to learn to program [closed]

  - by vanstee

  Possible Duplicate: What programming language should be taught in Computer Science 101? My girlfriend hates feeling completely out of the loop when my friends and I talk about anything related to computers, so she asked me to teach her how to program. I'm pretty happy she asked, but I want to be able to teach her enough to know the basics without her completely losing interest or getting too frustrated. She is a very smart girl, probably smarter than me, but her computer related skills are pretty minimal. What language should I teach her and why?

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• Is there a language with native pass-by-reference/pass-by-name semantics, which could be used in mod

  - by Bubba88

  Hi! This is a reopened question. I look for a language and supporting platform for it, where the language could have pass-by-reference or pass-by-name semantics by default. I know the history a little, that there were Algol, Fortran and there still is C++ which could make it possible; but, basically, what I look for is something more modern and where the mentioned value pass methodology is preferred and by default (implicitly assumed). I ask this question, because, to my mind, some of the advantages of pass-by-ref/name seem kind of obvious. For example when it is used in a standalone agent, where copyiong of values is not necessary (to some extent) and performance wouldn't be downgraded much in that case. So, I could employ it in e.g. rich client app or some game-style or standalone service-kind application. The main advantage to me is the clear separation between identity of a symbol, and its current value. I mean when there is no reduntant copying, you know that you're working with the exact symbol/path you have queried/received. And intristing boxing of values will not interfere with the actual logic of program. I know that there is C# ref keyword, but it's something not so intristic, though acceptable. Equally, I realize that pass-by-reference semantics could be simulated in virtually any language (Java as an instant example) and so on.. not sure about pass by name :) What would you recommend - create a something like DSL for such needs wherever it be appropriate; or use some languages that I already know? Maybe, there is something that I'm missing? Thank you!

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• Finding Local IP via Socket Creation / getsockname

  - by BSchlinker

  I need to get the IP address of a system within C++. I followed the logic and advice of another comment on here and created a socket and then utilized getsockname to determine the IP address which the socket is bound to. However, this doesn't appear to work (code below). I'm receiving an invalid IP address (58.etc) when I should be receiving a 128.etc Any ideas? string Routes::systemIP(){ // basic setup int sockfd; char str[INET_ADDRSTRLEN]; sockaddr* sa; socklen_t* sl; struct addrinfo hints, *servinfo, *p; int rv; memset(&hints, 0, sizeof hints); hints.ai_family = AF_UNSPEC; hints.ai_socktype = SOCK_DGRAM; if ((rv = getaddrinfo("4.2.2.1", "80", &hints, &servinfo)) != 0) { fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv)); return "1"; } // loop through all the results and make a socket for(p = servinfo; p != NULL; p = p->ai_next) { if ((sockfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol)) == -1) { perror("talker: socket"); continue; } break; } if (p == NULL) { fprintf(stderr, "talker: failed to bind socket\n"); return "2"; } // get information on the local IP from the socket we created getsockname(sockfd, sa, sl); // convert the sockaddr to a sockaddr_in via casting struct sockaddr_in *sa_ipv4 = (struct sockaddr_in *)sa; // get the IP from the sockaddr_in and print it inet_ntop(AF_INET, &(sa_ipv4->sin_addr.s_addr), str, INET_ADDRSTRLEN); printf("%s\n", str); // return the IP return str; }

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• How do you use stl's functions like for_each?

  - by thomas-gies

  I started using stl containers because they came in very handy when I needed functionality of a list, set and map and had nothing else available in my programming environment. I did not care much about the ideas behind it. STL documentations were only interesting up to the point where it came to functions, etc. Then I skipped reading and just used the containers. But yesterday, still being relaxed from my holidays, I just gave it a try and wanted to go a bit more the stl way. So I used the transform function (can I have a little bit of applause for me, thank you). From an academic point of view it really looked interesting and it worked. But the thing that boroughs me is that if you intensify the use of those functions, you need 10ks of helper classes for mostly everything you want to do in your code. The hole logic of the program is sliced in tiny pieces. This slicing is not the result of god coding habits. It's just a technical need. Something, that makes my life probably harder not easier. And I learned the hard way, that you should always choose the simplest approach that solves the problem at hand. And I can't see what, for example, the for_each function is doing for me that justifies the use of a helper class over several simple lines of code that sit inside a normal loop so that everybody can see what is going on. I would like to know, what you are thinking about my concerns? Did you see it like I do when you started working this way and have changed your mind when you got used to it? Are there benefits that I overlooked? Or do you just ignore this stuff as I did (and will go an doing it, probably). Thanks. PS: I know that there is a real for_each loop in boost. But I ignore it here since it is just a convenient way for my usual loops with iterators I guess.

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• Which way to store this data is effective?

  - by Tattat

  I am writing a game, which need a map, and I want to store the map. The first thing I can think of, is using a 2D-array. But the problem is what data should I store in the 2D-array. The player can tap different place to have different reaction. So, I am thinking store a 2D-array with objects, when player click some position, and I find it in the array, and use the object in that array to execute a cmd. But I have a concern that storing lots of object may use lots of memory. So, I am think storing char/int only. But it seems that not enough for me. I want to store the data like that: { Type:1 Color:Green } No matter what color is, if they are all type 1, the have same reactions in logic, but the visual effect is based on the color. So, it is not easy to store using a prue char/int data, unless I make something like this: 1-5 --> all type 1. 1=color green , 2=color red, 3 = color yellow.... ... 6-10 --> all type 2. 2 = color green, 2 = color red ... ... So, do you have any ideas on how to minimize the ram use, but also easy for me to read... ...thx

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• My 2009 MacBook Logic board failed - options to proceed and how difficult?

  - by user181061

  Scannerz just gave my MacBook logic board a big fat F! I upgraded from Snow Leopard to Mountain Lion about 3 weeks ago. The system was running short of memory so I upgraded it. The system was running fine for about 2 weeks. Yesterday the thing started acting erratic. A lot of spinning beach balls, delays, and then some errors saying files couldn't be read to or from the drive. I figured the drive was going because the system is over 3 years old. I ran Scannerz on it and it indicated a lot of errors and irregularities. I rescanned it in cursory mode, and none of them were repeatable, just showing up all over the place in different regions of the scan. I went through the docs and they implied either an I/O cable was bad, a connection was damaged, or the logic board was bad. I tossed on my backup of Snow Leopard that I cloned from the original hard drive because I figured Mountain Lion was to blame and booted from the USB drive with the clone on it. It wasn't. I performed scans on every single port, and errors and irregularities that couldn't be repeated were showing up on every single one of them. I then, for kicks, put a CD into the CD player. Scannerz doesn't test optical drives but I figured surely that will work. No it won't. More spinning beach balls and messages telling me it can't be read. It was working fine 3 days ago. I know a lot of people don't like MacBook's, but mine's been great, at least until now. It was working great even with Mountain Lion after the upgrade. The system is a mid-2009 MacBook. In my opinion, it's a complete waste to toss this system. The display is too good, the keyboard works great, and it still looks good, plus this type of MacBook still uses the FireWire 400 port and I use that for Time Machine backups. I've tried reseating the RAM, it didn't do anything. I shut the system down and put in the old RAM, booted to Snow Leopard, and the problems persist. Here are my questions: The Scannerz documentation somewhere said something about the Airport card not being seated properly, but when I go to iFixit, it's apparent, at least I think it's apparent, that this isn't a slot type Airport card that the user can easily install or remove. If the cables or connections to the Airport card are bad, could they be causing this problem. How about any other connections that can be intermittent, failing or erratic? Any type of resets that I could possibly do to get rid of this? For any of those that have replaced a logic board on a MacBook, if this really is the culprit, are there any "gotcha's" I need to be aware of? As an FYI, I replaced the hard drive on an old iBook @500MHz that I had a long time ago, and I replaced the drive on a 1.33GHz PowerBook about 6 years ago. You have to be careful, but using some of the info on web sites like iFixit it's not that hard. Time consuming, but not that hard. The Intel based MacBook's to me look like they're easier to service than either of those. I'm thinking about getting a unit off of eBay that matches mine but has something else wrong with it, like a busted display. I REFUSE to buy a new system. A guy at my office has a 2007 Mac Pro and he can't upgrade to Mountain Lion because his system is "obsoleted." That's ridiculous. If you pay nearly $7,500 for a system it shouldn't be trash just because Apple decides they don't have enough money (sorry for the soap box, but it's true, IMO!) Any input is appreciated.

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