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  • Using items in a list as arguments

    - by Travis Brown
    Suppose I have a function with the following type signature: g :: a -> a -> a -> b I also have a list of as—let's call it xs—that I know will contain at least three items. I'd like to apply g to the first three items of xs. I know I could define a combinator like the following: ($$$) :: (a -> a -> a -> b) -> [a] -> b f $$$ (x:y:z:_) = f x y z Then I could just use g $$$ xs. This makes $$$ a bit like uncurry, but for a function with three arguments of the same type and a list instead of a tuple. Is there a way to do this idiomatically using standard combinators? Or rather, what's the most idiomatic way to do this in Haskell? I thought trying pointfree on a non-infix version of $$$ might give me some idea of where to start, but the output was an abomination with 10 flips, a handful of heads and tails and aps, and 28 parentheses. (NB: I know this isn't a terribly Haskelly thing to do in the first place, but I've come across a couple of situations where it seems like a reasonable solution, especially when using Parsec. I'll certainly accept "don't ever do this in real code" if that's the best answer, but I'd prefer to see some clever trick involving the ((->) r) monad or whatever.)

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  • Appropriate high level language to deal with binary data

    - by fortran
    Hi, I need to write a small tool that parses a textual input and generates some binary encoded data. I would prefer to stay away from C and the like, in favour of a higher level, (optionally) safer, more expressive and faster to develop language. My language of choice for this kind of tasks usually is Python, but for this case dealing with binary raw data can be problematic if one isn't very careful with the numbers being promoted to bignums, sign extensions and such. Ideally I would like to have records with named bitfields that are portable to be serialised in a consistent manner. (I know that there's a strong point in doing it in a language I already master, although it isn't optimal, but I think this could be a good opportunity to learn something new). Thanks.

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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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  • 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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  • How do I split up a long value (32 bits) into four char variables (8bits) using C?

    - by Jordan S
    I have a 32 bit long variable, CurrentPosition, that I want to split up into 4, 8bit characters. How would I do that most efficiently in C? I am working with an 8bit MCU, 8051 architectecture. unsigned long CurrentPosition = 7654321; unsigned char CP1 = 0; unsigned char CP2 = 0; unsigned char CP3 = 0; unsigned char CP4 = 0; // What do I do next? Should I just reference the starting address of CurrentPosition with a pointer and then add 8 two that address four times? It is little Endian. ALSO I want CurrentPosition to remain unchanged.

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  • Interview question: difference between object and object-oriented languages.

    - by Bar
    My friend was asked the following question: what's the difference between object language and object-oriented language? It's a little unintelligible question. What does term «object language» correspond to? Does that mean «pure» object-oriented language, like the Wikipedia article says: Languages called "pure" OO languages, because everything in them is treated consistently as an object, from primitives such as characters and punctuation, all the way up to whole classes, prototypes, blocks, modules, etc. They were designed specifically to facilitate, even enforce, OO methods. Examples: Smalltalk, Eiffel, Ruby, JADE, VB.NET.

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  • How to add site search function to website using XHTML/HTML?

    - by felixd68
    I really want to learn how to make my own search engine for my site. I have the defined buttons and labels, but it doesn't search. I can't figure out the HTML or XHTML code for actually searching the site. This is the code I have so far: <p class="search"> <label>SEARCH</label> <input name="search" type="text" class="txt" /> <input name="search-btn" type="submit" class="btn" value="SEARCH" /> </p> Thanks!

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  • sending a packet to multiple client at a time from udp socket

    - by mawia
    Hi! all, I was trying to write a udp server who send an instance of a file to multiple clients.Now suppose any how I manage to know the address of those client statically(for the sake of simplicity) and now I want to send this packet to these addresses.So how exactly I need to fill the sockaddr structure to contain the address of these clients.I am taking an array of sockaddr structure(to contain client address) and trying to send at each one them at a time.Now problem is to fill the individual sockaddr structure to contain the client address. I was trying to do something like that sa[1].sin_family = AF_INET; sa[1].sin_addr.s_addr = htonl(INADDR_ANY);//should'nt I replace this INADDR_ANY with client ip?? sa[1].sin_port = htons(50002); Correct me if this is not the correct way. All your help in this regard will be highly appreciated. With Thanks in advance, Mawia

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  • Are there equivalents to Ruby's method_missing in other languages?

    - by Justin Ethier
    In Ruby, objects have a handy method called method_missing which allows one to handle method calls for methods that have not even been (explicitly) defined: Invoked by Ruby when obj is sent a message it cannot handle. symbol is the symbol for the method called, and args are any arguments that were passed to it. By default, the interpreter raises an error when this method is called. However, it is possible to override the method to provide more dynamic behavior. The example below creates a class Roman, which responds to methods with names consisting of roman numerals, returning the corresponding integer values. class Roman def romanToInt(str) # ... end def method_missing(methId) str = methId.id2name romanToInt(str) end end r = Roman.new r.iv #=> 4 r.xxiii #=> 23 r.mm #=> 2000 For example, Ruby on Rails uses this to allow calls to methods such as find_by_my_column_name. My question is, what other languages support an equivalent to method_missing, and how do you implement the equivalent in your code?

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  • How do you tell if a string contains another string in Unix shell scripting?

    - by Matt
    Hi all, I want to write a Unix shell script that will do various logic if there is a string inside of another string. For example, if I am in a certain folder, branch off. Could someone please tell me how to accomplish this? If possible I would like to make this not shell specific (i.e. not bash only) but if there's no other way I can make do with that. #!/bin/sh CURRENT_DIR=`pwd` if [ CURRENT_DIR contains "String1" ] then echo "String1 present" elif [ CURRENT_DIR contains "String1" ] then echo "String2 present" else echo "Else" fi

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  • c# GUI changing a listbox from another class

    - by SlowForce
    I've written a multithreaded server that uses tcplistener and a client handler class that controls input and output. I also have a GUI chat client. The chat client works fine and the console version of the server also works well. I have a start() method in the partial(?) Form class, which I run from a new thread when I click a button, that starts the TCP Listener and loops through and accepts socket requests. For every request a new ClientHandler object is created and the socket is passed to this object before being used in a new handler thread. The ClientHandler is a different class to the form and I'm having real problems writing data to the Listbox in the Form class from within the ClientHandler class. I've tried a few different ways of doing this but none of them work as they involve creating a new form class within the ClientHandler. Any help or advice on what I should be reading to help me would be really appreciated.

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  • International JRE6 or JDK6 or reading a file in "cp037" encoding scheme

    - by Reddy
    I have been trying to read a file in "cp037" encoding scheme using JAVA. I able to read a file in basic encoding schemes like UTF-8, UTF16 etc...After a bit of research on the internet i came to know that we need charset.jar or international version of JRE be installed to support extended encoding schemes. Can anyone send me a link for international version of JRE6 or JDK6. or is there any better way that i could read a file in cp037 encoding scheme. P.S: cp037 is a character encoding scheme supported by IBM Mainframes. All i need is to display a file in windows, which is being generated on IBM Mainframes machine, using a java program. Thanks in advance for your help... :-)

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  • java statistics collection for performance evaluation

    - by user384706
    What is the most efficient way to collect and report performance statistic analysis from an application? If I have an application that uses a series of network apis, and I want to report statistics at runtime, e.g. Method doA() was called 3 times and consumed on avg 500ms Method doB() was called 5 times and consumed on avg 1200ms etc Then, I thought of using a well defined data structure (of collection) that each thread updates per remote call, and this can be used for the report. But I think that it will make the performance worse, for the time spend for statistics collection. Am I correct? How would I procceed if I used a background thread for this, and the other threads that did the remote calls were unaware of this collection gathering? Thanks

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  • Is there a suitable replacement for C++, when I would like to write video processing applications?

    - by Nisanio
    Hi I want to write a video editing software, and the "logical" conclusion is that the language I must to use is C++... But I don't like it (sorry c++ fans) I would like to write it with something cool, like Lisp or Haskell or Erlang... But I don't know if the open source implementation of those languages (I don't have money to buy licenses) let me made a competitive software (in the performance area) What do you think? what do you recommend?

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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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  • How can I dial the default connection on Pocket PC 2003 ?

    - by Jalil
    I am working on a PPC2003 application. The devices on which the application has to run have a modem and VPN connection set. I want to automatically dial the system default "work" connection, which is the VPN one, which dial the modem one first. The user has another application who does automatically make the system dial the default connection. But I can't undertand how to do it from my Compact .NET application. I tried using OpenNETCF net package, but I could not make it work.

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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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