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  • Right rotate of tree in Haskell: how is it work?

    - by Roman
    I don't know haskell syntax, but I know some FP concepts (like algebraic data types, pattern matching, higher-order functions ect). Can someone explain please, what does this code mean: data Tree ? = Leaf ? | Fork ? (Tree ?) (Tree ?) rotateR tree = case tree of Fork q (Fork p a b) c -> Fork p a (Fork q b c) As I understand, first line is something like Tree-type declaration (but I don't understand it exactly). Second line includes pattern matching (I don't understand as well why do we need to use pattern matching here). And third line does something absolutely unreadable for non-haskell developer. I've found definition of Fork as fork (f,g) x = (f x, g x) but I can't move further anymore.

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  • Template function as a template argument

    - by Kos
    I've just got confused how to implement something in a generic way in C++. It's a bit convoluted, so let me explain step by step. Consider such code: void a(int) { // do something } void b(int) { // something else } void function1() { a(123); a(456); } void function2() { b(123); b(456); } void test() { function1(); function2(); } It's easily noticable that function1 and function2 do the same, with the only different part being the internal function. Therefore, I want to make function generic to avoid code redundancy. I can do it using function pointers or templates. Let me choose the latter for now. My thinking is that it's better since the compiler will surely be able to inline the functions - am I correct? Can compilers still inline the calls if they are made via function pointers? This is a side-question. OK, back to the original point... A solution with templates: void a(int) { // do something } void b(int) { // something else } template<void (*param)(int) > void function() { param(123); param(456); } void test() { function<a>(); function<b>(); } All OK. But I'm running into a problem: Can I still do that if a and b are generics themselves? template<typename T> void a(T t) { // do something } template<typename T> void b(T t) { // something else } template< ...param... > // ??? void function() { param<SomeType>(someobj); param<AnotherType>(someotherobj); } void test() { function<a>(); function<b>(); } I know that a template parameter can be one of: a type, a template type, a value of a type. None of those seems to cover my situation. My main question is hence: How do I solve that, i.e. define function() in the last example? (Yes, function pointers seem to be a workaround in this exact case - provided they can also be inlined - but I'm looking for a general solution for this class of problems).

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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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  • Using function arguments to dynamically generate a query

    - by Varun
    I am working on an issue management system, developed in PHP/MySQL. It requires search functionality, where the user will mention the search parameters and based on these parameters the system will return the result set. To solve this I am trying to write a function and all the user selected parameters are passed as arguments. Based on the arguments I will dynamically generate the query. Sample Query: select * from tickets inner join ticket_assigned_to on tickets.id=ticket_assigned_to.ticket_id where tickets.project_id= in ('') and tickets.status in ('') and ticket_assigned_to.user_id in ('') and tickets.reporter_user_id='' and tickets.operator_user_id in ('') and tickets.due_date between '' and '' and tickets.ts_created between '' and ''; I also need to handle cases where the arguments can be ORed or ANDed in the query. For example: select * from tickets inner join ticket_assigned_to on tickets.id=ticket_assigned_to.ticket_id where tickets.project_id= in ('') and tickets.status in ('') or tickets.due_date = '' or tickets.ts_created between '' and ''; I am also planning to use the same function at other places in the project also. Like to display all the tickets of a user or all tickets created between given dates and so on... How to handle this situation? Should I go with a single function which handles all this or numerous small functions? Need guidance here.

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  • Manifesto for Integrated Development Environments

    - by Hugo S Ferreira
    Have you recently take a peek at Coda, or Espresso, or Textmate? Or even Google Chrome's Developer Tools? They are well designed, intuitive, interface rich, and extensible. But Coda, Espresso or Textmate, among several, are text editors, not IDEs. On the other side, VIM and Emacs live in the last century, and Eclipse is an overbloated platform. This is more like an outcry for a decent, common infrastructure for REAL IDEs. But there's some questions attached: (i) what features are needed for such a product and (ii) what products are out there that could fullfil this need, and what are they missing. So here's my draft for a manifesto: Manifesto for Integrated Development Environments: We favor interactivity and productivity over syntax and tools. We favor inline, contextual documentation over man and html files. We favor high-definition, graphic-capable color screens over 80x25 character terminals. We favor the use of advanced input schemas over unintuitive keyboard shortcuts. We favor a common, extensible and customizable infrastructure over unmaintained chaintools. We know the difference between search&replace and refactoring. We know the difference between integrated debugging support over a terminal window. We know the difference between semantic-aware code-completion over dumb textual templates. We favor the usage of standards like (E)BNF.

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  • By-name repeated parameters

    - by Green Hyena
    How to pass by-name repeated parameters in Scala? The following code fails to work: scala> def foo(s: (=> String)*) = { <console>:1: error: no by-name parameter type allowed here def foo(s: (=> String)*) = { ^ Is there any other way I could pass a variable number of by name parameters to the method?

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  • How to create symbolic links in Windows?

    - by guillermooo
    Related: In .NET, how do I Create a Junction in NTFS, as opposed to a Symlink? I've tried Winbolic (Windows XP), but i can't get it to work the way I want. Am I wrong here?: If I create a symbolic link within a folder in my %PATH%, the referenced directory should work as if it had actually been added to %PATH%, right?

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  • For distributed applications, which to use, ASIO vs. MPI?

    - by Rhubarb
    I am a bit confused about this. If you're building a distributed application, which in some cases may perform parallel operations (although not necessarily mathematical), should you use ASIO or something like MPI? I take it MPI is a higher level than ASIO, but it's not clear where in the stack one would begin.

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  • [PHP] Dynamic cron jobs?

    - by Frankie Laguna
    I'm writing a script that needs to be called at a random time during the day, but am not sure how to accomplish this. I don't want to waste server resources to run a cron job every minute. I want the script to be called at random, so generating the random times for say a month in advance and then creating cron jobs for each of them isn't what I'm looking for. Also this script only needs to be executed once a day. Thanks in advance!

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  • How to use boost::transform_iterator to iterate over modifed std::map values?

    - by Frank
    I have an std::map, and I would like to define an iterator that returns modified values. Typically, a std::map<int,double>::iterator iterates over std::pair<int,double>, and I would like the same behavior, just the double value is multiplied by a constant. I tried it with boost::transform_iterator, but it doesn't compile: #include <map> #include <boost/iterator/transform_iterator.hpp> #include <boost/functional.hpp> typedef std::map<int,double> Map; Map m; m[100] = 2.24; typedef boost::binder2nd< std::multiplies<double> > Function; typedef boost::transform_iterator<Function, Map::value_type*> MultiplyIter; MultiplyIter begin = boost::make_transform_iterator(m.begin(), Function(std::multiplies<double>(), 4)); // now want to similarly create an end iterator // and then iterate over the modified map The error is: error: conversion from 'boost ::transform_iterator< boost::binder2nd<multiplies<double> >, gen_map<int, double>::iterator , boost::use_default, boost::use_default >' to non-scalar type 'boost::transform_iterator< boost::binder2nd<multiplies<double> >, pair<const int, double> * , boost::use_default, boost::use_default >' requested What is gen_map and do I really need it? I adapted the transform_iterator tutorial code from here to write this code ...

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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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  • How do you encrypt data between client and server running in Flash and Java?

    - by ArmlessJohn
    We have a multiclient system where the client is written in Flash and the server is written in Java. Currently, communication is done in Flash by usage of flash.net.Socket and the protocol is written in JSON. The server uses a custom port to receive connections and then proceed to talk with each client. As expected, data is sent and received on both fronts as raw bytes, which are then decoded as needed. We would like to encrypt the communication between clients and server. I have some basic understanding about public/private key encryption, but I do not know what is the best way to exchange keys or what libraries are available (on both languages) to do this. What would be the best strategy to attack this problem and where should I start looking for libraries/methods to implement this encryption?

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  • scheme2lisp::define function and pass it as parameter

    - by Stas
    Hi! Im need translate some code from scheme to common lisp. Now I have something like this (defun sum (term a next b) (if (> a b) 0 (+ (term a) (sum term (next a) b)))) (defun sum-int (a b) (defun (ident x) x ) (sum ident a 1+ b)) But it doesn't interprete with out errors. * - DEFUN: the name of a function must be a symbol, not (IDENT X) Help me plese. Thanks

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  • What is your company's stance on Developers using Laptops?

    - by codepunk
    I am a developer and my company is moving towards a "no laptop" policy in fear of them being lost or stolen and source code being compromised. Now I don't work for NASA, the military or anything labeled Top Secret but our code is very important to our business nonetheless (as all source code would be). I'll be honest, I disagree with this policy against laptops and wanted to see what others think. I'd like to know: What is your team/company's stance on laptops Your company's size and/or field (small, medium or large, Fortune 500, etc). Whether you've had to take any extra precautions (signing any additional legal, ensure your hard drive is encrypted, etc). Thanks!

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  • Static and Dynamic Scooping Problem

    - by Devyn
    Hi, I'm solving following code in Static and Dynamic Scooping. I got following answer but I need someone to confirm if I'm correct or not since I'm a bit confusing. I really appreciate if anyone can explain in simple way! Static => (1)8 (2)27 Dynamic => (1)10 (2)27 proc main var x,y,z; proc sub1 var x,z x := 6; z := 7; sub2; x := y*z + x; print(x); ---- (2) end; proc sub2 var x,y x := 1; y := x+z+2; print(y); ---- (1) end; begin x := 1; y:=3; z:=5; sub1; end

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  • using object in multiple function

    - by nixon
    Hi. How can i use object from one function in another ? main() { private void button1_click { MyClass object = new MyClass(); object.blabla(); } private void button2_click { // how can i use object from button1_click ?? } }

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