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  • Generics and Constrained Polymorphism versus Subtyping

    - by Rahul G
    Hullo all. In this (Warning: PDF) presentation on Haskell Type Classes, on slide #54, there's this question: Open Question: In a language with generics and constrained polymorphism, do you need subtyping too? My questions are: How do generics and constrained polymorphism make subtyping unnecessary? If generics and constrained polymorphism make subtyping unnecessary, why does Scala have subtyping?

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  • Rewriting Live TCP Streams

    - by user213060
    I want to rewrite TCP/IP streams. Ettercap's etterfilter command lets you perform simple live replacements of TCP/IP data based on fixed strings or regexes. Example: http://ettercap.sourceforge.net/forum/viewtopic.php?t=2833 I would like to rewrite streams based on my own filter program instead of just simple string replacements. Anyone have an idea of how to do this? Is there anything other than Ettercap that can do live replacement like this, maybe as a plugin to a VPN software or something? Thanks!

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  • how does pipe work

    - by lego69
    hello, explain me please how exactly pipe works, for example I have this snippet of the code set line = ($<) while(${#line} != 0) if(${#line} == 5) then echo line | sort | ./calculate ${1} endif set line = ($<) end I need to choose all rows with 5 words and after sort it and after transfer, but I'm confused, how will it work, first of all 'while' will take all information and after that transfer it to sort, or every iteration 'while' will do sort? thanks in advance

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  • Examples of useful or non-trival dual interfaces

    - by Scott Weinstein
    Recently Erik Meijer and others have show how IObservable/IObserver is the dual of IEnumerable/IEnumerator. The fact that they are dual means that any operation on one interface is valid on the other, thus providing a theoretical foundation for the Reactive Extentions for .Net Do other dual interfaces exist? I'm interested in any example, not just .Net based.

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  • How can i uniquely identify users trying to open() a kernel module?

    - by user349072
    Dear Gurus, I'm working on a Kernel module and i'm trying to Uniquely identify each one of the users trying to open() the module ( can be either processes or threads ). what is the best way to identify them? is there an ID i can get from a system call? i wish to get all users in a list that specifies whether they're trying to open the module for read \ write and i need to know which one tried acting... many many thanks. in regards, IK

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  • Why is the software world full of status codes?

    - by David V McKay
    Why did programmers ever start using status codes? I mean, I guess I could imagine this might be useful back in the days when a text string was an expensive resource. WAYYY back then. But even after we had megabytes of memory to work with, we continued to use them. What possible advantage could there be for obfuscating the meaning of an error message or status message behind a status code?

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  • Functional languages targeting the LLVM

    - by Matthew
    Are there any languages that target the LLVM that: Are statically typed Use type inference Are functional (i.e. lambda expressions, closures, list primitives, list comprehensions, etc.) Have first class object-oriented features (inheritance, polymorphism, mixins, etc.) Have a sophisticated type system (generics, covariance and contravariance, etc.) Scala is all of these, but only targets the JVM. F# (and to some extent C#) is most if not all of these, but only targets .NET. What similar language targets the LLVM?

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  • How to migrate existing udp application to raw sockets

    - by osgx
    Hello Is there a tutorial for migration from plain udp sockets (linux, C99/C++, recv syscall is used) to the raw sockets? According to http://aschauf.landshut.org/fh/linux/udp_vs_raw/ch03s04.html raw socket is much faster than udp. Application is client-server. client is proprietary and must use exactly same procotol as it was with udp server. But server can be a bit faster with raw sockets. What parts of udp I must to implement in server? Is there a "quick migration" libraries?

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  • Need help in understanding the mapping of user-space send, sendto, sendmsg to kernel-space sendmsg

    - by bala1486
    Hello, I am trying to implement my own transport layer protocol in Linux for an experiment. I am going to use socket interface and add my protocol using sock_register. For the proto_ops i can see that the parameters for the sendmsg and recvmsg are (struct kiocb *iocb, struct socket *sock, struct msghdr *msg, size_t len, int flags). But there are three types of user api's send, sendto, sendmsg. Of these three only sendmsg contains a parameter for msghdr. I find that the other two api's are incompatible with the parameters supplied by the kernel to my kernel-space sendmsg function. So what happens when we use send and sendto user-space api's? Hope i am clear.. Thanks, Bala

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  • Are Scala "continuations" just a funky syntax for defining and using Callback Functions?

    - by Alex R
    And I mean that in the same sense that a C/Java for is just a funky syntax for a while loop. I still remember when first learning about the for loop in C, the mental effort that had to go into understanding the execution sequence of the three control expressions relative to the loop statement. Seems to me the same sort of effort has to be applied to understand Continuations (in Scala and I guess probably other languages). And then there's the obvious follow-up question... if so, then what's the point? It seems like a lot of pain (language complexity, programmer errors, unreadable programs, etc) for no gain.

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  • Truly declarative language?

    - by gjvdkamp
    Hi all, Does anyone know of a truly declarative language? The behaviour I'm looking for is kind of what Excel does, where I can define variables and formulas, and have the formula's result change when the input changes (without having set the answer again myself) The behaviour I'm looking for is best shown with this pseudo code: X = 10 // define and assign two variables Y = 20; Z = X + Y // declare a formula that uses these two variables X = 50 // change one of the input variables ?Z // asking for Z should now give 70 (50 + 20) I've tried this in a lot of languages like F#, python, matlab etc, but every time i try this they come up with 30 instead of 70. Wich is correct from an imperative point of view, but i'm looking for a more declerative behaviour if you know what i mean. And this is just a very simple calculation. When things get more difficult it should handle stuff like recursion and memoization automagically. The code below would obviously work in C# but it's just so much code for the job, i'm looking for something a bit more to the point without all that 'technical noise' class BlaBla{ public int X {get;set;} // this used to be even worse before 3.0 public int Y {get;set;} public int Z {get{return X + Y;}} } static void main(){ BlaBla bla = new BlaBla(); bla.X = 10; bla.Y = 20; // can't define anything here bla.X = 50; // bit pointless here but I'll do it anyway. Console.Writeline(bla.Z);// 70, hurray! } This just seems like so much code, curly braces and semicolons that add nothing. Is there a language/ application (apart from Exel) that does this? Maybe I'm no doing it right in the mentioned langauges, or I've completely missed an app that does just this. I prototyped a language/ application that does this (along with some other stuff) and am thinking of productizing it. I just can't believe it's not there yet. Don't want to waste my time. Thanks in advance, Gert-Jan

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  • How do i write tasks? (parallel code)

    - by acidzombie24
    I am impressed with intel thread building blocks. I like how i should write task and not thread code and i like how it works under the hood with my limited understanding (task are in a pool, there wont be 100 threads on 4cores, a task is not guaranteed to run because it isnt on its own thread and may be far into the pool. But it may be run with another related task so you cant do bad things like typical thread unsafe code). I wanted to know more about writing task. I like the 'Task-based Multithreading - How to Program for 100 cores' video here http://www.gdcvault.com/sponsor.php?sponsor_id=1 (currently second last link. WARNING it isnt 'great'). My fav part was 'solving the maze is better done in parallel' which is around the 48min mark (you can click the link on the left side. That part is really all you need to watch if any). However i like to see more code examples and some API of how to write task. Does anyone have a good resource? I have no idea how a class or pieces of code may look after pushing it onto a pool or how weird code may look when you need to make a copy of everything and how much of everything is pushed onto a pool.

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  • How to maintain a persistant network-connection between two applications over a network?

    - by John
    I was recently approached by my management with an interesting problem - where I am pretty sure I am telling my bosses the correct information but I really want to make sure I am telling them the correct stuff. I am being asked to develop some software that has this function: An application at one location is constantly processing real-time data every second and only generates data if the underlying data has changed in any way. On the event that the data has changed send the results to another box over a network Maintains a persistent connection between the both machines, altering the remote box if for some reason the network connection went down From what I understand, I imagine that I need to do some reading on doing some sort of TCP/IP socket-level stuff. That way if the connection is dropped the remote location will be aware that the data it has received may be stale. However management seems to be very convinced that this can be accomplished using SOAP. I was under the impression that SOAP is more or less a way for a client to initiate a procedure from a server and get some results via the HTTP protocol. Am I wrong in assuming this? I haven't been able to find much information on how SOAP might be able to solve a problem like this. I feel like a lot of people around my office are using SOAP as a buzzword and that has generated a bit of confusion over what SOAP actually is - and is capable of. Any thoughts on how to accomplish this task would be appreciated!

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  • Using MonadPlus in FRP.Reactive.FieldTrip

    - by ony
    I'm studying FRP at this moment through FieldTrip adaptor. And hit the problem with strange way of frames scheduling and integration. So now I'm trying to build own marker Event for aligning Behaviour stepping. So... flipflop :: Behavior String flipflop = stepper "none" (xflip 2) where xflip t0 = do t <- withTimeE_ (atTime t0) return "flip" `mplus` xflop (t+3) xflop t0 = do t <- withTimeE_ (atTime t0) return "flop" `mplus` xflip (t+2) txtGeom = ((uscale2 (0.5::Float) *%) . utext . show <$>) main = anim2 (txtGeom . pure flipflop) Questions is: Why this example leads to memory leak? Is there safe way to build sequence of events where each next one is scheduled depending on previous?

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  • How do i write task? (parallel code)

    - by acidzombie24
    I am impressed with intel thread building blocks. I like how i should write task and not thread code and i like how it works under the hood with my limited understanding (task are in a pool, there wont be 100 threads on 4cores, a task is not guaranteed to run because it isnt on its own thread and may be far into the pool. But it may be run with another related task so you cant do bad things like typical thread unsafe code). I wanted to know more about writing task. I like the 'Task-based Multithreading - How to Program for 100 cores' video here http://www.gdcvault.com/sponsor.php?sponsor_id=1 (currently second last link. WARNING it isnt 'great'). My fav part was 'solving the maze is better done in parallel' which is around the 48min mark (you can click the link on the left side). However i like to see more code examples and some API of how to write task. Does anyone have a good resource? I have no idea how a class or pieces of code may look after pushing it onto a pool or how weird code may look when you need to make a copy of everything and how much of everything is pushed onto a pool.

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  • Translate imperative control flow with break-s/continue-s to haskell

    - by dorserg
    Consider the following imperative code which finds the largest palindrome among products of 3-digit numbers (yes, it's the one of the first tasks from "Project of [outstanding mathematician of 18th century]" site): curmax = 0 for i in range(999,100): for j in range(999,100): if ((i*j) < curmax): break if (pal(i*j)): curmax = i*j break print curmax As I'm learning Haskell currently, my question is, how do you translate this (and basically any imperative construct that contains something more complex than just plain iteration, e.g. breaks, continues, temporary variables and all this) to Haskell? My version is maxpal i curmax | i < 100 = curmax | otherwise = maxpal (i-1) (innerloop 999) where innerloop j | (j < 100) || (p < curmax) = curmax | pal p = p | otherwise = innerloop (j-1) where p = i*j main = print $ maxpal 999 0 but this looks like we're still in imperative uglytown. So what could you advise, what are the approaches of dealing with such cases FP-style?

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  • First Come, First Served process scheduling

    - by user253530
    i have 4 processes: p1 - bursts 5, priority: 3 p2 - bursts 8, priority: 2 p3 - bursts 12, priority: 2 p4 - bursts 6, priority: 1 Assuming that all processes arrive at the scheduler at the same time what is the average response time and average turnaround time? For FCFS is it ok to have them in the order p1, p2, p3, p4 in the execution queue?

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  • Rewriting Live TCP/IP (Layer 4) (i.e. Socket Layer) Streams

    - by user213060
    I have a simple problem which I'm sure someone here has done before... I want to rewrite Layer 4 TCP/IP streams (Not lower layer individual packets or frames.) Ettercap's etterfilter command lets you perform simple live replacements of Layer 4 TCP/IP streams based on fixed strings or regexes. Example ettercap scripting code: if (ip.proto == TCP && tcp.dst == 80) { if (search(DATA.data, "gzip")) { replace("gzip", " "); msg("whited out gzip\n"); } } if (ip.proto == TCP && tcp.dst == 80) { if (search(DATA.data, "deflate")) { replace("deflate", " "); msg("whited out deflate\n"); } } http://ettercap.sourceforge.net/forum/viewtopic.php?t=2833 I would like to rewrite streams based on my own filter program instead of just simple string replacements. Anyone have an idea of how to do this? Is there anything other than Ettercap that can do live replacement like this, maybe as a plugin to a VPN software or something? I would like to have a configuration similar to ettercap's silent bridged sniffing configuration between two Ethernet interfaces. This way I can silently filter traffic coming from either direction with no NATing problems. Note that my filter is an application that acts as a pipe filter, similar to the design of unix command-line filters: >[eth0] <----------> [my filter] <----------> [eth1]< What I am already aware of, but are not suitable: Tun/Tap - Works at the lower packet layer, I need to work with the higher layer streams. Ettercap - I can't find any way to do replacements other than the restricted capabilities in the example above. Hooking into some VPN software? - I just can't figure out which or exactly how. libnetfilter_queue - Works with lower layer packets, not TCP/IP streams. Again, the rewriting should occur at the transport layer (Layer 4) as it does in this example, instead of a lower layer packet-based approach. Exact code will help immensely! Thanks!

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  • Why did you decide "against" using Erlang?

    - by Zubair
    Have you actually "tried" (means programmed in, not just read an article on it) Erlang and decided against it for a project? If so, why? Also, if you have opted to go back to your old language, or to use another functional language like F#, Haskell, Clojure, Scala, or something else then this counts too, and state why.

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  • Does a good programmer need to have good spatial sense?

    - by lisa1234
    Do you need to have good spatial sense to be a good programmer? I have next to nothing of it (I think it has to do with the differing vision of my eyes). I've already coded quite little things but wonder if this interferes with the ability to 'imagine' the assembly of the code in case of a more complex program? Sorry for my english, I'm Austrian and not so used to write in English.. Thanks for your ansers..

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  • Listening Port Permanently. if file is on my stream, Get file. How to?

    - by Phsika
    i writed 2 client and server program. client dend file also server listen port and than get file.But i need My server App must listen on 51124 port permanently. if any file on my stream, show my message "there is a file on your stream" and than show me savefile dialog. But my server app in "Infinite loop". 1) listen 51124 port every time 2) do i have a file on my stream, show me a messagebox. private void Form1_Load(object sender, EventArgs e) { TcpListener Dinle = new TcpListener(51124); try { Dinle.Start(); Socket Baglanti = Dinle.AcceptSocket(); if (!Baglanti.Connected) { MessageBox.Show("No Connection!"); } else { while (true) { byte[] Dizi = new byte[250000]; Baglanti.Receive(Dizi, Dizi.Length, 0); string Yol; saveFileDialog1.Title = "Save File"; saveFileDialog1.ShowDialog(); Yol = saveFileDialog1.FileName; FileStream Dosya = new FileStream(Yol, FileMode.Create); Dosya.Write(Dizi, 0, Dizi.Length - 20); Dosya.Close(); listBox1.Items.Add("dosya indirildi"); listBox1.Items.Add("Dosya Boyutu=" + Dizi.Length.ToString()); listBox1.Items.Add("Indirilme Tarihi=" + DateTime.Now); listBox1.Items.Add("--------------------------------"); } } } catch (Exception) { throw; } } My Algorithm: if(AnyFileonStream()==true) { GetFile() //Also continue to listening 51124 port... } How can i do that?

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