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• How to learn Haskell

  - by anderstornvig

  For a few days I've tried to wrap my head around the functional programming paradigm in Haskell. I've done this by reading tutorials and watching screencasts, but nothing really seems to stick. Now, in learning various imperative/OO languages (like C, Java, PHP), excercises have been a good way for me to go. But since I don't really know what Haskell is capable of and because there are many new concepts to utilize, I haven't known where to start. So, how did you learn Haskell? What made you really "break the ice"? Also, any good ideas for beginning excercises?

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• Determine cluster size of file system in Python

  - by Philip Fourie

  I would like to calculate the "size on disk" of a file in Python. Therefore I would like to determine the cluster size of the file system where the file is stored. How do I determine the cluster size in Python? Or another built-in method that calculates the "size on disk" will also work. I looked at os.path.getsize but it returns the file size in bytes, not taking the FS's block size into consideration. I am hoping that this can be done in an OS independent way...

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• memristor is a new paradigm (fourth element in integrated circuits)? [closed]

  - by lsalamon

  The memristor will bring a new paradigm of programming, opened enormous opportunities to enable the machines to gain knowledge, creating a new paradigm toward the intelligence altificial. Do you believe that we are paving the way for the era of intelligent machines? More info about : Brain-like systems? "As for the human brain-like characteristics, memristor technology could one day lead to computer systems that can remember and associate patterns in a way similar to how people do. This could be used to substantially improve facial recognition technology or to provide more complex biometric recognition systems that could more effectively restrict access to personal information. These same pattern-matching capabilities could enable appliances that learn from experience and computers that can make decisions." [EDITED] The way is open. News on the subject Brain-Like Computer Closer to Realization

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• What's going on with my server? High load, lots of idle CPU time, low disk utilization

  - by Jonathan

  I run a web site and send a legitimate opt-in, daily email newsletter to subscribers. Both the web hosting and email sending are done by the same machine. I have about 100,000 subscribers who have opted in to my daily email newsletter. My PHP script did a pretty good job sending mail to all of them until fairly recently, but as the list has grown I can't keep up. When I run top, I have very high load--usually at least 6 or 7, sometimes as high as 15--even though I only have two CPUs. However, when I run sar, my CPU is idle an average of about 30% of the time. So, it seems I'm not CPU bound. When I run iostat, it seems as though I'm not disk bound because my %util for each device is very low (no more than 5%). Given that I don't seem to be CPU bound or disk bound, why is top reporting such high load? Additionally, since I don't seem to be CPU bound or disk bound, why is my email sending script not able to keep up? Here's what I see when running top: top - 11:33:28 up 74 days, 18:49, 2 users, load average: 7.65, 8.79, 8.28 Tasks: 168 total, 5 running, 162 sleeping, 0 stopped, 1 zombie Cpu(s): 38.9%us, 58.6%sy, 0.8%ni, 0.0%id, 0.7%wa, 0.2%hi, 0.8%si, 0.0%st Mem: 3083012k total, 2144436k used, 938576k free, 281136k buffers Swap: 2048248k total, 39164k used, 2009084k free, 1470412k cached Here's what I see when running iostat -mx: avg-cpu: %user %nice %system %iowait %steal %idle 34.80 1.20 55.24 0.37 0.00 8.38 Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await svctm %util sda 0.19 71.70 1.59 29.45 0.02 0.07 5.90 0.55 17.82 1.16 3.59 sda1 0.00 0.00 0.00 0.00 0.00 0.00 7.10 0.00 13.80 13.72 0.00 sda2 0.05 50.45 1.13 24.57 0.01 0.29 24.25 0.35 13.43 1.15 2.97 sda3 0.05 10.17 0.20 2.33 0.01 0.05 43.75 0.05 20.96 2.45 0.62 sda4 0.00 0.00 0.00 0.00 0.00 0.00 2.00 0.00 70.50 70.50 0.00 sda5 0.07 0.22 0.03 0.07 0.00 0.00 32.84 0.08 856.19 8.03 0.08 sda6 0.02 5.45 0.03 0.72 0.00 0.02 67.55 0.02 26.72 5.26 0.39 sda7 0.00 1.56 0.00 0.42 0.00 0.01 38.04 0.00 8.88 5.84 0.24 sda8 0.01 3.84 0.20 1.35 0.00 0.02 28.55 0.05 31.90 4.08 0.63 Here's what I see when running sar: 09:40:02 AM CPU %user %nice %system %iowait %steal %idle 09:50:01 AM all 30.59 1.01 49.80 0.23 0.00 18.37 10:00:08 AM all 31.73 0.92 51.66 0.13 0.00 15.55 10:10:06 AM all 30.43 0.99 48.94 0.26 0.00 19.38 10:20:01 AM all 29.58 1.00 47.76 0.25 0.00 21.42 10:30:01 AM all 29.37 1.02 47.30 0.18 0.00 22.13 10:40:06 AM all 32.50 1.01 52.94 0.16 0.00 13.39 10:50:01 AM all 30.49 1.00 49.59 0.15 0.00 18.77 11:00:01 AM all 29.43 0.99 47.71 0.17 0.00 21.71 11:10:07 AM all 30.26 0.93 49.48 0.83 0.00 18.50 11:20:02 AM all 29.83 0.81 48.51 1.32 0.00 19.52 11:30:06 AM all 31.18 0.88 51.33 1.15 0.00 15.47 Average: all 26.21 1.15 42.62 0.48 0.00 29.54 Here are the top handful of processes listed at the particular time I happened to run top -c: PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 8180 mysql 16 0 57448 19m 2948 S 26.6 0.7 4702:26 /usr/sbin/mysqld --basedir=/ --datadir=/var/lib/mysql --user=mysql --pid-file=/var/lib/mysql/bristno.pid --skip-external-locking 26956 brristno 17 0 0 0 0 Z 8.0 0.0 0:00.24 [php] <defunct> 26958 brristno 17 0 94408 43m 37m R 5.0 1.4 0:00.15 /usr/bin/php /home/brristno/public_html/dbv.php 22852 nobody 16 0 9628 2900 1524 S 0.7 0.1 0:00.17 /usr/local/apache/bin/httpd -k start -DSSL 8591 brristno 34 19 96896 13m 6652 S 0.3 0.4 0:29.82 /usr/local/bin/php /home/brristno/bin/mailer.php 1qwqyb6 i0gbor 24469 nobody 16 0 9628 2880 1508 S 0.3 0.1 0:00.08 /usr/local/apache/bin/httpd -k start -DSSL 25495 nobody 15 0 9628 2876 1500 S 0.3 0.1 0:00.06 /usr/local/apache/bin/httpd -k start -DSSL 26149 nobody 15 0 9628 2864 1504 S 0.3 0.1 0:00.04 /usr/local/apache/bin/httpd -k start -DSSL

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• Program LED with just USB port

  - by LifeH2O

  I want to control LED with C# using only USB port. I don't want to attach any other device with USB. I just want to attach LED directly to USB port pins and program it (blink etc). How can i do that? I am new to hardware programming and it will be my first program. EDIT: I can do it already (blink LED) using printer port by attaching one led pin to data pin and other to ground. How can i do the same with USB port? My motherboard does not have a printer port. USB is the only option.

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• Must a Language that Implements Monads be Statically Typed?

  - by Morgan Cheng

  I am learning functional programming style. From this link http://channel9.msdn.com/shows/Going+Deep/Brian-Beckman-Dont-fear-the-Monads/, Brian Beckman gave a brilliant introduction about Monad. He mentioned that Monad is about composition of functions so as to address complexity. A Monad includes a unit function that transfers type T to an amplified type M(T); and a Bind function that, given function from T to M(U), transforms type M(T) to another type M(U). (U can be T, but is not necessarily). In my understanding, the language implementing monad should be type-checked statically. Otherwise, type errors cannot be found during compilation and "Complexity" is not controlled. Is my understanding correct?

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• Is there a smart web developer language skill combination?

  - by Cryo

  I'm no newbie to programming, but I'm making the move to a career in web development, and I've noticed that so many job postings have different combinations of skill requirements: (PHP, C#, XML, XHTML/CSS, ASP, .NET, jQuery, YUI, Joomla, Ruby, Perl, Python, Java, Javascript... the list goes on.) As of now, I've started learning XHTML, CSS, JavaScript, jQuery, PHP, and mySQL, but with so many combinations, I want to plan ahead to have a marketable combination of skills as early on as possible. Am I on the right path? What is vital for a marketable web programmer's arsenal? Thanks for your thoughts.

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• Debugging in visual studio 2008 freezes entire system

  - by mat690

  Any time i try to debug in visual studio 2008 my entire system will freeze whenever a breakpoint is hit. I can move the mouse around and that remains responsive but nothing i click on does anything, I can bring up the task manager but can't do anything with it and i am able to lock/unlock the machine. I tried a fix that i found via google that suggested i disable advanced text services but it didn't work. I am using visual studio 2008 with SP1 running on Windows XP Pro, asking here is my last hope before formating/reinstalling so i hope someone can help me out. I debug by running the application in debug mode, the freeze happens no matter what the project size and it seems as if it is just the entire GUI that freezes, the computer carries on working just fine i just can't do anything with it because the GUI is totaly unresponsive.

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• writing to a file in nasm using system calls

  - by yurib

  As part of an assignment I'm supposed to write to a file using system calls. Everything works fine except when I try to open the file in gedit (linux), it says it can't identify the character encoding. Notepad (on windows) opens the file just fine. Why doesn't it work on linux ? here's the code: section .text global _start _start: mov EAX, 8 mov EBX, filename mov ECX, 0700 int 0x80 mov EBX, EAX mov EAX, 4 mov ECX, text mov EDX, textlen int 0x80 mov EAX, 6 int 0x80 mov eax, 1 int 0x80 section .data filename db "./output.txt", 0 text db "hello world", 0 textlen equ $ - text thanks :)

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• How to implement a mailing system with Rails that sends emails in the background

  - by Tam

  I want to implement a reliable mailing system with Ruby on Rails that sends emails in the background as sending email sometimes takes like 10 seconds or more so I don't want the user to wait. Some ideas I thought of: 1- Write to a table in DB a have a background process that go over and send email (concern: potential many reads/writes to DB slows down my application) 2- Messaging Queue background process / Rake task (concern: if server crashes queued mails will be lost also might eat up a lot of memory if many emails) I was wondering if you a know of a good solution that provides a balance between reliability and performance.

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• Scrum for Team System 2010 - How to use story points instead of Hours

  - by dretzlaff17

  I have installed TFS 2010 using the Scrum for Team System v3. The work item templates want you to enter a Project Backlog Item that includes story points, then you need to add linked tasks as a child of the PBI. It is at the task level where you can assign team individuals, update estimated hours left, etc. What is the importance of the Story Points used at the PBI item if individual tasks are using hours? Has anyone customized this template so that the child work item tasks use story point burn downs instead of hours? Also, I would be nice to have the total number of story points from each individual task roll up into the PBI item as a read only field for total story points. Thanks for your time.

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• Strange client's address returned throug accept(..) function.

  - by Negai

  Hi everyone, I'm a socket programming newbie. Here's a snippet: struct sockaddr_storage client_addr; ... client_addr_size = sizeof(client_addr); client_socket = accept( server_socket, (struct sockaddr *)&client_addr, &client_addr_size ); ... result = inet_ntop( AF_INET, &((struct sockaddr_in *)&client_addr)->sin_addr, client_addr_str, sizeof(client_addr_str) ); Whenever the client connects the address I get is 0.0.0.0 regardless from the host. Can anybody explain, what I'm doing wrong? Thanks.

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• Visual C++/CLI "An unhandled exception of type 'System.StackOverflowException' occurred in"

  - by JennyWong

  Hi, I have a game I am making, it is giving me this message... "An unhandled exception of type 'System.StackOverflowException' occurred in game.exe" To explain...I have a 2D array with 9 different opening moves and I am getting a random number to use as the array reference to retrieve the details needed for a move... you may get the same move again - but that's illegal. the move may be illegal for other reasons too So to try and fix this, I am calling the function again from within the function. The error occurs very randomly Is this bad practise to call a function from within itself? What would be a better way to randomly row from a 2D array, AND if it isn't accept to get another one.... Or better still, how can I retrieve a random LEGAL move?

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• Why does GetTextFace always return "system"?

  - by user545142

  I am trying to get the font of controls in other applications. When I try WM_GETFONT, it returns 0. This my code: [DllImport("User32.DLL")] public static extern IntPtr SendMessage(IntPtr hWnd, int Msg, int wParam, int lParam); IntPtr fx = SendMessage(button1.Handle, 0x31, 0, 0); When I use GetTextFace with a button, it always returns "system". This is my code: StringBuilder Buff = new StringBuilder(256); IntPtr dc = GetDCEx(button1.Handle, IntPtr.Zero, DeviceContextValues.Window |DeviceContextValues.Cache | DeviceContextValues.ClipSiblings | DeviceContextValues.IntersectRgn); IntPtr hfont = GetTextFace(dc, 256, Buff); Of course I'm sure I changed the font type. How can I solve this problem? I am using C# under Windows 7.

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• Photo printing API system?

  - by webdestroya

  I am looking for options to provide customers on my website a way to order prints for photos. (It is a photo sharing site, so it needs to be automated, I don't want any portfolio sites that require uploads and what not). Basically it just needs where I send them the photos, the address, (and possibly billing info) and they make the prints and mail them out. I have searched all over the place for such a system, but none seem to offer what I want. I tried hacking snapfish (which worked, but it says "Return to Picasa" on the buttons, which makes it sort of lame...) Any ideas?

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• O'Reilly book clarification on 2d linear system

  - by Eric

  The Oreilly book "Learning openCV" states at page 356 : Quote Before we get totally lost, let’s consider a particular realistic situation of taking measurements on a car driving in a parking lot. We might imagine that the state of the car could be summarized by two position variables, x and y, and two velocities, vx and vy. These four variables would be the elements of the state vector xk. Th is suggests that the correct form for F is: x = [ x; y; vx; vy; ]k F = [ 1, 0, dt, 0; 0, 1, 0, dt; 0, 0, 1, 0; 0, 0, 0, 1; ] It seems natural to put 'dt' just there in the F matrix but I just don't get why. What if I have a n states system, how would I spray some "dt" in the F matrix?

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• Operating system question

  - by ual

  I recently asked myself: If a program, like Mozilla Firefox for example, is started - the control must be somehow given to it. But when the program crashes, why doesn't my whole system crash like in early Windows version? How can Windows take back the control from the program, or even not give it to it fully? (Note: This is not my homework; I go to school but in my informatics class are really only guys that would answer with "Can I eat that?" when I ask them about kernels. Same with my teacher.)

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• Operating system scheduler question

  - by ual

  I recently asked myself: If a program, like Mozilla Firefox for example, is started - the control must be somehow given to it. But when the program crashes, why doesn't my whole system crash like in early Windows version? How can Windows take back the control from the program, or even not give it to it fully? (Note: This is not my homework; I go to school but in my informatics class are really only guys that would answer with "Can I eat that?" when I ask them about kernels. Same with my teacher.)

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• linux's fork and system resources

  - by Dmitry Bespalov

  Suppose I have following code in linux: int main() { FILE* f = fopen("file.txt", "w"); fork(); fwrite("A", 1, 1, f); fclose(f); return 0; } What I know about fork from documentation, is that it makes the copy of current process. It copies state of the memory as well, so *f should be equal in both instances. But what happens with system resources, such as a file handle? In this example I open the file with write intentions, so only one instance can write into file, right? Which of the instances will actually write into file? Who should care further about the file handle, and call fclose() ?

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• University System Automation, how the internal system of a university works?

  - by Zia ur Rahman

  Hay dear! Suppose we want to make a software , we want to automate the system of university. Suppose a student apply in the university for a certain course, now the question is where the application form of the student will go and what process will be done on this form and then what is the next stage of this form and why it will go to the next stage? Now I hope you have got my point. I need information from the enrollment of a student to its pass out. Or provide a state transition diagram or Data flow diagram. I will be very thankful.

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• How to create a language these days?

  - by Mike

  I need to get around to writing that programming language I've been meaning to write. How do you kids do it these days? I've been out of the loop for over a decade; are you doing it any differently now than we did back in the pre-internet, pre-windows days? You know, back when "real" coders coded in C, used the command line, and quibbled over which shell was superior? Just to clarify, I mean, not how do you DESIGN a language (that I can figure out fairly easily) but how do you build the compiler and standard libraries and so forth? What tools do you kids use these days?

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• How do you learn a class hierarchy quickly?

  - by rsteckly

  Hi, Something I don't enjoy about programming is learning a new API. For example, right now I'm trying to learn Windows Identity Foundation. Its frustrating because I'm going to spend the bulk of the time learning how a few classes work and actually only write several lines of code. In .NET, there are so many types that I seem to spend more time hunting around in msdn for a class than writing code. It also interrupts my workflow while I'm working because I have to type a little bit than look something up. Obviously, I don't have to do this for the basic classes. Whenever new things come though there is definitely some looking up to do. Then I often don't reuse that class enough to really review it or bring it into action. I'm wondering if anybody out there has a found a way to memorize (or look up more efficiently) these object model hierarchies?

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• How few a files does it take to load a program on Linux?

  - by BCS

  The (hypothetical for now) situation is the user of my system is going to be given a chunk of C code and needs my system to compile and run it in a chroot sandbox that is generated on the fly and I want to require the fewest files in the box as possible. I'm only willing to play with compiler and linker settings (e.g. static link everything I can expect to be able to find) and make some moderate restriction on what the code can expect use (e.g. they can't use arbitrary libs). The question is how simple can I get the sandbox. Clearly I need the executable, but what about an ELF loader and a .so for the system calls? Can I dump either of them and is there something else I'll need?

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• System.Linq.Dynamic and DateTime

  - by Matthew Hood

  I am using System.Linq.Dynamic to do custom where clauses from an ajax call in .Net MVC 1.0. It works fine for strings, int etc but not for DateTime, I get the exception cannot compare String to DateTime. The very simple test code is items = items.Where(string.Format(@" {0} {1}{2}{1} ", searchField, delimiter, searchString)); Where searchField will be for example start_date and the data type is DateTime, delimiter is " (tried with nothing as well) and searchString will be 01-Jan-2009 (tried with 01/01/2009 as well) and items is an IQueryable from LinqToSql. Is there a way of specifying the data type in a dynamic where, or is there a better approach. It is currently already using some reflection to work out what type of delimiter is required.

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• Pure functional bottom up tree algorithm

  - by Axel Gneiting

  Say I wanted to write an algorithm working on an immutable tree data structure that has a list of leaves as its input. It needs to return a new tree with changes made to the old tree going upwards from those leaves. My problem is that there seems to be no way to do this purely functional without reconstructing the entire tree checking at leaves if they are in the list, because you always need to return a complete new tree as the result of an operation and you can't mutate the existing tree. Is this a basic problem in functional programming that only can be avoided by using a better suited algorithm or am I missing something?

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