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  • Prolog: using the sort/2 predicate

    - by Øyvind Hauge
    So I'm trying to get rid of the wrapper clause by using the sort library predicate directly inside split. What split does is just generating a list of numbers from a list that looks like this: [1:2,3:2,4:6] ---split-- [1,2,3,2,4,6]. But the generated list contains duplicates, and I don't want that, so I'm using the wrapper to combine split and sort, which then generates the desired result: [1,2,3,4,6]. I'd really like to get rid of the wrapper and just use sort within split, however I keep getting "ERROR: sort/2: Arguments are not sufficiently instantiated." Any ideas? Thanks :) split([],[]). split([H1:H2|T],[H1,H2|NT]) :- split(T,NT). wrapper(L,Processed) :- split(L,L2), sort(L2,Processed).

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  • Android HTTP Connection

    - by Ubersoldat
    Can anybody tell my why this doesn't work in the Android emulator? From the browser I have access and the server is internal. All I can think of is that I'm missing some configuration on my app so it can access the network layer. try { InetAddress server = Inet4Address.getByName("thehost"); //Doesn't work either //or InetAddress server2 = Inet4Address.getByAddress(new String("192.168.1.30").getBytes()); if(server.isReachable(5000)){ Log.d(TAG, "Ping!"); } Socket clientsocket = new Socket(server, 8080); } catch (UnknownHostException e) { Log.e(TAG, "Server Not Found"); } catch (IOException e) { Log.e(TAG, "Couldn't open socket"); } Throws an UnknownHostException Thanks

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  • If-statement with logical OR

    - by exiter2000
    public class Test{ public static void main(String args[]){ int a = 0; int b = 1; int c = 10; if ( a == 0 || b++ == c ){ a = b + c; }else{ b = a + c; } System.out.println("a: " + a + ",b: " + b + ",c: " + c); } } Ok, this is Java code and the output is a: 11,b: 1,c: 10 And I believe the C acts same as Java in this case That is because second condition(b++ == c) would never executed if the first condition is true in 'OR' operator. There is a "NAME" for this. I just don't remember what it is. Does anyone know what this is called?? Thanks in advance

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  • How do "modern JVMs" differ from older JVMs?

    - by Lord Torgamus
    Here's a phrase that I heard a lot throughout high school and university computer science classes: "That's not an issue for modern JVMs." Usually this would come up in discussions about overall performance or optimization strategies. It was always treated as a kind of magical final answer, though, as if it makes issues no longer worth thinking about. And that just leads me to wonder: what are the differences between the prototypical "modern JVM" and older JVMs, really?

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  • design pattern tools to use?

    - by ajsie
    i have noticed that every area has some tools you can use to make things easier. eg. css = dreamweaver doctrine/propel = orm designer // you dont have to hardcore code schemas manually and remembering all the syntax/variables mysql = mysql workbench // the same etc. in this way you get aided and dont have to type things the hard way, and can learn the structure, but then use GUI tools to help you develop faster. now i'm learning design patterns (singleton, factory, command, memento etc) and im wondering if there are some kind of tools you can use that will help you develop faster. i dont know exactly what tools i'm trying to find, just helping me when coding with design patterns (schema drawings? references?) are there any?

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  • Java - how to tell class of an object?

    - by lkm
    Given a method that accepts as a parameter a certain supertype. Is there any way, within that method, to determine the actual class of the object that was passed to it? I.e. if a subtype of the allowable parameter was actually passed, is there a way to find out which type it is? If this isn't possible can someone explain why not (from a language design perspective)? Thanks Update: just to make sure I was clear void doSomething(MyType myType) { //determine if myType is MyType OR one of its subclasses } Since the method signature specifies the parameter as being MyType, then how can one tell if the object is actually a subtype of MyType (and which one).

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  • Are raw C++ pointers first class objects?

    - by Shailesh Kumar
    According to Wikipedia: An object is first-class when it: can be stored in variables and data structures can be passed as a parameter to a subroutine can be returned as the result of a subroutine can be constructed at runtime has intrinsic identity (independent of any given name) Somebody had once told me that raw pointers are not first class objects while smart pointers like std::auto_ptr are. But to me, a raw pointer (to an object or to a function) in C++ does seem to me to satisfy the conditions stated above to qualify as a first class object. Am I missing something?

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  • Do you think the AI industry will ever come back?

    - by Isaiah
    I just spent some time reading about the collapse of the AI industry and realized a lot of the reason it failed was because technology was slow to catch up with their theories on when it would be available. I also read that it is believed computers that will be able to emulate human synapses may be made round 2015-2025. It's 2010 now and were getting pretty close to that time frame. I was wondering if anyone thinks that the AI industry will return as the technology lands? And if so, will it change the language market? Could Lisp like languages suddenly experience a burst of growth if it does? Idk I just thought it was interesting thinking about it.

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  • Is Python a beginner language or is it robust?

    - by orokusaki
    I am already working on some software in Python but I'm having one of those days where I step back and reflect just to make sure I'm not spinning my wheels. I know that Twitter launched with RoR because it was fast to build. Then they almost moved into another language in 2008 because of scalability issues. This has caused me to step back and introspect for a moment to make sure I'm heading down the right path. I've read in some tutorials and other places that Python is "a great first language" or a "nice beginner language" as though it's not capable of larger tasks. I look at it as Python can do what Java or ASP can but with about 1/4th of the code, not to mention I don't have to build or compile, etc. I've read that Java runs quite a few times faster than Python which is important of course, but then I read everywhere that hardware keeps getting cheaper and there are projects like Unladen Swallow by Google to make Python faster. Should I be concerned or is this just the remnants of Java developers?

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  • simple question on C

    - by lego69
    I have this snippet of the code char *str = “123”; if(str[0] == 1) printf("Hello\n"); why I can't receive my Hello thanks in advance! how exactly compiler does this comparison if(str[0] == 1)?

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  • functional, bind1st and mem_fun

    - by Neil G
    Why won't this compile? #include <functional> #include <boost/function.hpp> class A { A() { typedef boost::function<void ()> FunctionCall; FunctionCall f = std::bind1st(std::mem_fun(&A::process), this); } void process() {} }; Errors: In file included from /opt/local/include/gcc44/c++/bits/stl_function.h:712, from /opt/local/include/gcc44/c++/functional:50, from a.cc:1: /opt/local/include/gcc44/c++/backward/binders.h: In instantiation of 'std::binder1st<std::mem_fun_t<void, A> >': a.cc:7: instantiated from here /opt/local/include/gcc44/c++/backward/binders.h:100: error: no type named 'second_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h:103: error: no type named 'first_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h:106: error: no type named 'first_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h:111: error: no type named 'second_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h:117: error: no type named 'second_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h: In function 'std::binder1st<_Operation> std::bind1st(const _Operation&, const _Tp&) [with _Operation = std::mem_fun_t<void, A>, _Tp = A*]': a.cc:7: instantiated from here /opt/local/include/gcc44/c++/backward/binders.h:126: error: no type named 'first_argument_type' in 'class std::mem_fun_t<void, A>' In file included from /opt/local/include/boost/function/detail/maybe_include.hpp:13, from /opt/local/include/boost/function/detail/function_iterate.hpp:14, from /opt/local/include/boost/preprocessor/iteration/detail/iter/forward1.hpp:47, from /opt/local/include/boost/function.hpp:64, from a.cc:2: /opt/local/include/boost/function/function_template.hpp: In static member function 'static void boost::detail::function::void_function_obj_invoker0<FunctionObj, R>::invoke(boost::detail::function::function_buffer&) [with FunctionObj = std::binder1st<std::mem_fun_t<void, A> >, R = void]': /opt/local/include/boost/function/function_template.hpp:913: instantiated from 'void boost::function0<R>::assign_to(Functor) [with Functor = std::binder1st<std::mem_fun_t<void, A> >, R = void]' /opt/local/include/boost/function/function_template.hpp:722: instantiated from 'boost::function0<R>::function0(Functor, typename boost::enable_if_c<boost::type_traits::ice_not::value, int>::type) [with Functor = std::binder1st<std::mem_fun_t<void, A> >, R = void]' /opt/local/include/boost/function/function_template.hpp:1064: instantiated from 'boost::function<R()>::function(Functor, typename boost::enable_if_c<boost::type_traits::ice_not::value, int>::type) [with Functor = std::binder1st<std::mem_fun_t<void, A> >, R = void]' a.cc:7: instantiated from here /opt/local/include/boost/function/function_template.hpp:153: error: no match for call to '(std::binder1st<std::mem_fun_t<void, A> >) ()'

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  • Efficient algorithm to distribute work?

    - by Zwei Steinen
    It's a bit complicated to explain but here we go. We have problems like this (code is pseudo-code, and is only for illustrating the problem. Sorry it's in java. If you don't understand, I'd be glad to explain.). class Problem { final Set<Integer> allSectionIds = { 1,2,4,6,7,8,10 }; final Data data = //Some data } And a subproblem is: class SubProblem { final Set<Integer> targetedSectionIds; final Data data; SubProblem(Set<Integer> targetedSectionsIds, Data data){ this.targetedSectionIds = targetedSectionIds; this.data = data; } } Work will look like this, then. class Work implements Runnable { final Set<Section> subSections; final Data data; final Result result; Work(Set<Section> subSections, Data data) { this.sections = SubSections; this.data = data; } @Override public void run(){ for(Section section : subSections){ result.addUp(compute(data, section)); } } } Now we have instances of 'Worker', that have their own state sections I have. class Worker implements ExecutorService { final Map<Integer,Section> sectionsIHave; { sectionsIHave = {1:section1, 5:section5, 8:section8 }; } final ExecutorService executor = //some executor. @Override public void execute(SubProblem problem){ Set<Section> sectionsNeeded = fetchSections(problem.targetedSectionIds); super.execute(new Work(sectionsNeeded, problem.data); } } phew. So, we have a lot of Problems and Workers are constantly asking for more SubProblems. My task is to break up Problems into SubProblem and give it to them. The difficulty is however, that I have to later collect all the results for the SubProblems and merge (reduce) them into a Result for the whole Problem. This is however, costly, so I want to give the workers "chunks" that are as big as possible (has as many targetedSections as possible). It doesn't have to be perfect (mathematically as efficient as possible or something). I mean, I guess that it is impossible to have a perfect solution, because you can't predict how long each computation will take, etc.. But is there a good heuristic solution for this? Or maybe some resources I can read up before I go into designing? Any advice is highly appreciated!

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  • Career Path Choices (Education)

    - by sandy101
    I am in the final year of bca from md university. I am not sure with my career and very confused with the question of should I do MCA or MBA? Can any one help me on this question? I want to know the options available to me, and I also want to know the various colleges which provide MCA and what are the further prospects thereafter!

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  • Property value of a String object in JavaScript

    - by naivists
    As far as I understand, every string is an object in Javascript. Still, it "does not work" as I expect it to be: var a="abc"; //here we get a new string object a.b = 123; //I seem to declare a property "b" of that object alert(a.b); //alerts "undefined" However, if I try to define a string in the "wrong way", everything works as expected var a=new String("abc"); // a.b = 123; alert(a.b); //alerts "123" Why is that so?

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  • What coding standards do you follow?

    - by Mark Szymanski
    I was just curious what coding standards people followed. I for one use the following: Brackets ALWAYS go on the next line. For instance: int main() { //Blah... } I never use code folding. (Yes my IDE's do support it (Xcode and Eclipse). Put related functions/methods single-spaced, otherwise double space. Here is an example: int foo = 0; printf("%d",foo); those are related while these are not: printf("Hello, World!"); return(0); I don't put else statements on the same line as the closing bracket for the preceding if statement. Most of the time in Java if a program needs multiple try catch statements I will just put the whole thing in one try catch.

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  • How do you manage tasks within your work?

    - by Michael
    Just wondering how you all manage your workload effectively when there's a lot of your plate? What do you do to break it down into bite-size chunks and how do you track progress of each task? Do you find TDD helps to focus your attention of getting areas of functionality complete before moving onto the next one? I quite often find myself getting a bit overwhelmed when I have an involving task on the go (even if it can be broken down into lots of small chunks), even though I know I'm more than capable of doing the work. We have a kind of agile approach Interested to hear how everyone manages things effectively.

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