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  • What is your favourite cleverly written functional code?

    - by sdcvvc
    What are your favourite short, mind-blowing snippets in functional languages? My two favourite ones are (Haskell): powerset = filterM (const [True, False]) foldl f v xs = foldr (\x g a -> g (f a x)) id xs v -- from Hutton's tutorial (I tagged the question as Haskell, but examples in all languages - including non-FP ones - are welcome as long as they are in functional spirit.)

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  • Is Haskell "mainstream", or is it mainly used by hobbyists and academics?

    - by Asher
    I came across a post where someone wrote something inaccurate about Haskell (won't go into it) and he got flammed for it. Which (pleasantly) surprised me. About 3 years ago I read this joke about Haskell: All the haskell programmers in the world can fit into a 747 and if that plane were to crash no one would care... or something along those lines. Which brings me to my question: how healthy is the Haskell community, anyway? Is Haskell "mainstream"? Is it mainly used by hobbiest and academics or someone making some serious money from it (which is the true yardstick of how good a language is - just kidding, geez!)?

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  • Are there any tools for performing static analysis of Scala code?

    - by Roman Kagan
    Are there any tools for performing static analysis of Scala code, similar to FindBugs and PMD for Java or Splint for C/C++? I know that FindBugs works on the bytecode produced by compiling Java, so I'm curious as to how it would work on Scala. Google searches (as of 27 October 2009) reveal very little. Google searches (as of 01 February 2010) reveal this question.

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  • What is the right approach to checksumming UDP packets

    - by mr.b
    I'm building UDP server application in C#. I've come across a packet checksum problem. As you probably know, each packet should carry some simple way of telling receiver if packet data is intact. Now, UDP already has 2-byte checksum as part of header, which is optional, at least in IPv4 world. Alternative method is to have custom checksum as part of data section in each packet, and to verify it on receiver. My question boils down to: is it better to rely on (optional) checksum in UDP packet header, or to make a custom checksum implementation as part of packet data section? Perhaps the right answer depends on circumstances (as usual), so one circumstance here is that, even though code is written and developed in .NET on Windows, it might have to run under platform-independent Mono.NET, so eventual solution should be compatible with other platforms. I believe that custom checksum algorithm would be easily portable, but I'm not so sure about the first one. Any thoughts? Also, shouts about packet checksumming in general are welcome.

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  • [Perl] Testing for EAGAIN / EWOULDBLOCK on a recv

    - by Robert S. Barnes
    I'm testing a socket to see if it's still open: my $dummy = ''; my $ret = recv($sock, $dummy, 1, MSG_DONTWAIT | MSG_PEEK); if (!defined $ret || (length($dummy) == 0 && $! != EAGAIN && $! != EWOULDBLOCK )) { logerr("Broken pipe? ".__LINE__." $!"); } else { # socket still connected, reuse logerr(__LINE__.": $!"); return $sock; } I'm passing this code a socket I know for certain is open and it's always going through the first branch and logging "Broken pipe? 149 Resource temporarily unavailable". I don't understand how this is happening since "Resource temporarily unavailable" is supposed to correspond to EAGAIN as far as I know. I'm sure there must be something simple I'm missing. And yes, I know this is not a full proof way to test and I account for that.

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  • Delphi On Windows

    - by j-t-s
    Hi All I have decided (whether it's for better or for worse), to start learning Delphi. But, Is it available in Visual Studio? Or is there an IDE for it? I googled Delphi, but came up with some really weird sites. Thanks Jason

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  • How to print "Hello, world!" (in every possible way)

    - by Attila Oláh
    Here's what I', trying to do: 1 language: (Python < 3): print "Hello, world!" 2 languages: (Python < 3 & Windows Shell, aka .bat file): rem=""" echo "Hello, world!" exit """ print "Hello, world!" Next step could be something like bash. Since the above one raises an exception, I tried to make it not raise exceptions, like this: rem=""" echo "Hello, world!" exit """ exit="" exit print "Hello, world!" The only issue is, of course, it won't print the hello world. And I really want it to print that hello world for me. Anyone can help with this? Also, any other language would do it, just don't break the previous ones (i.e. the answer still has to be valid Python code and print out the nice hello world greeting when run with Python.) Any ideas are welcome. I'm making this a community wiki so feel free to add ideas to the list.

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  • Confusion regarding laziness

    - by Abhinav Kaushik
    I have a function myLength = foldl (\ x _ -> x + 1) 0 which fails with stack overflow with input around 10^6 elements (myLength [1..1000000] fails). I believe that is due to the thunk build up since when I replace foldl with foldl', it works. So far so good. But now I have another function to reverse a list : myReverse = foldl (\ acc x -> x : acc) [] which uses the lazy version foldl (instead of foldl') When I do myLength . myReverse $ [1.1000000]. This time it works fine. I fail to understand why foldl works for the later case and not for former?

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  • Testing Async downloads with ASIHTTPRequest

    - by Baishampayan Ghose
    I am writing a simple library using ASIHTTPRequest where I am fetching URLs in an async manner. My problem is that the main function that I have written to test my lib exits before the async calls are finished. I am very new to Obj C and iPhone development, can anyone suggest a good way to wait before all the requests are finished in the main function? Currently, my main function looks like this - int main(int argc, char *argv[]) { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; IBGApp *ibgapp = [[IBGApp alloc] init]; IBGLib *ibgl = [[IBGLib alloc] initWithUsername:@"joe" andPassword:@"xxx"]; // The two method calls below download URLs async. [ibgl downloadURL:@"http://yahoo.com/" withRequestDelegate:ibgapp andRequestSelector:@selector(logData:)]; [ibgl downloadURL:@"http://google.com/" withRequestDelegate:ibgapp andRequestSelector:@selector(logData:)]; [pool release]; return 0; // I reach here before the async calls are done. } So what is the best way to wait till the async calls are done? I tried putting sleep, but obviously doesn't work.

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  • Accessing type members outside the class in Scala

    - by Pekka Mattila
    Hi, I am trying to understand type members in Scala. I wrote a simple example that tries to explain my question. First, I created two classes for types: class BaseclassForTypes class OwnType extends BaseclassForTypes Then, I defined an abstract type member in trait and then defined the type member in a concerete class: trait ScalaTypesTest { type T <: BaseclassForTypes def returnType: T } class ScalaTypesTestImpl extends ScalaTypesTest { type T = OwnType override def returnType: T = { new T } } Then, I want to access the type member (yes, the type is not needed here, but this explains my question). Both examples work. Solution 1. Declaring the type, but the problem here is that it does not use the type member and the type information is duplicated (caller and callee). val typeTest = new ScalaTypesTestImpl val typeObject:OwnType = typeTest.returnType // declare the type second time here true must beTrue Solution 2. Initializing the class and using the type through the object. I don't like this, since the class needs to be initialized val typeTest = new ScalaTypesTestImpl val typeObject:typeTest.T = typeTest.returnType // through an instance true must beTrue So, is there a better way of doing this or are type members meant to be used only with the internal implementation of a class?

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  • Software Development Lifecycle

    - by j-t-s
    Hi All Our investor wants a SDLC. I've never written one before, and I don't have enough time to go and buy a book, or spend much time learning about them. But from what I'vebeen told about them, is basically that you need to list requirements (what needs to be done), and list what has already been done. Is this correct? thank you

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  • Measuring Programmers' Productivity. Bad, good or invasive?

    - by Fraga
    A client needs my company to develop an app that will be able to measure the programmer productivity, by getting information from VS, IE, SSMS, profiler and VMware. For example: Lines, Methods, Classes (Added, Deleted, Modified) How many time spent in certain file, class, method, specific task, etc. How many time in different stages of the development cycle (Design, Coding, Debugging, Compiling, Testing) Real lines of code. Etc They told me they want to implement PSP. Would you resign if a company wants to measure this way? OR Would you install this kind of software for self improvement?

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  • Communication protocols in UDP

    - by Betamoo
    After many hours, I have discovered that the given udp server needs the following steps for a successful communication: 1- Send "Start Message" on a given port 2- Wait to receive from server on any port 3- Then the port dedicated to you to send further data to the server equals the port you have received on it + 1 So I am asking if this kind is a known protocol/handshaking, or it is only special to this server?? PS: All above communication were in udp sockets in C# PS: Related to a previous question: http://stackoverflow.com/questions/2757868/about-c-udp-sockets Thanks

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  • how/resources to compile a procedural language into [sql]

    - by Philip
    I am looking into the possibility/feasibility/resources for building a cross compiler which takes a procedural or Object Oriented language like C, or Java and compiling it into SQL. I understand that the advantage of SQL code is performing set operations which is fundamentally different from procedural languages which generally process 1 at a time. If anyone has done this before, or if it is thought of as too complicated to do or any other ideas/concerns/suggestions would be greatly appreciated. Thanks in advance Philip

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  • Difference between 'scope' and 'namespace'?

    - by katriel
    What is the difference, in general, between the concepts of namespaces and scope? To my understanding, both describe the parts of a program in which a variable/object/method/function will be accessible. I understand that 'scope' tends to be a property of the variable (e.g., "This variable has global scope"), while a 'namespace' is a property of the program (e.g., "A Python function creates a local namespace"). Are there other differences? Global scope vs global namespace addresses a slightly narrower question: global namespaces in C++. http://www.alan-g.me.uk/tutor/tutname.htm states, There are a few very subtle differences between the terms but only a Computer Scientist pedant would argue with you, and for our purposes namespace and scope are identical. What are those subtle differences? Under what circumstances or with which kinds of languages do people use each concept?

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  • Quantum PSO and Charged PSO (PSO = Particle Swarm Optimizer)

    - by The Elite Gentleman
    Hi Guys I need to implement PSO's (namely charged and quantum PSO's). My questions are these: What Velocity Update strategy do each PSO's use (Synchronous or Asynchronous particle update) What social networking topology does each of the PSO's use (Von Neumann, Ring, Star, Wheel, Pyramid, Four Clusters) For now, these are my issues. All your help will be appreciated. Thanks.

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  • Multiple Socket Connections

    - by BSchlinker
    I need to write a server which accepts connections from multiple client machines, maintains track of connected clients and sends individual clients data as necessary. Sometimes, all clients may be contacted at once with the same message, other times, it may be one individual client or a group of clients. Since I need confirmation that the clients received the information and don't want to build an ACK structure for a UDP connection, I decided to use a TCP streaming method. However, I've been struggling to understand how to maintain multiple connections and keep them idle. I seem to have three options. Use a fork for each incoming connection to create a separate child process, use pthread_create to create an entire new thread for each process, or use select() to wait on all open socket IDs for a connection. Recommendations as to how to attack this? I've begun working with pthreads but since performance will likely not be an issue, multicore processing is not necessary and perhaps there is a simpler way.

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