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  • HTML - Correct way of coding a checkbox with a Label.

    - by egarcia
    I've been using formtastic in order to generate HTML forms on rails applications. My question, however, is really HTML-related. Today I found a strange behaviour on the way formtastic generates checkboxes (fields of type :boolean on formtastic lingo). The rest of the fields (non-checkboxes) are generated this way: <li> <label for="my_textbox_field">My TextBox</label> <input id="my_textbox_field" type="text" ... > </li> Checkboxes, however, are enclosed inside their <label> tags completely - like this: <li> <label for="my_boolean_field"> <input id="my_boolean_field" type="checkbox" ... > This is my boolean field </label> </li> Formtastic phylosophy seems to be based on the Learning to Love Forms presentation. In effect, on slide 36 of that presentation this structure is suggested for checkboxes. I guess in the presentation itself the presenter explained why this was done, but it is not written on the slides. Can anyone tell me why enclosing checkboxes inside their <label> tag might be a good idea, as opposed to putting them outside, like with textboxes?

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  • Can't send client certificate via SslStream

    - by Jonathan
    I am doing an SSL3 handshake using an SslStream, but, in spite of my best efforts, the SslStream never sends a client certificate on my behalf. Here is the code: SSLConnection = new System.Net.Security.SslStream(SSLInOutStream, false, new System.Net.Security.RemoteCertificateValidationCallback(AlwaysValidRemoteCertificate), new System.Net.Security.LocalCertificateSelectionCallback(ChooseLocalCertificate)); X509CertificateCollection CC = new X509CertificateCollection(); CC.Add(Org.BouncyCastle.Security.DotNetUtilities.ToX509Certificate(MyLocalCertificate)); SSLConnection.AuthenticateAsClient("test", CC, System.Security.Authentication.SslProtocols.Ssl3, false); and then I have AlwaysValidRemoteCertificate just returning true, and ChooseLocalCertificate returning the zeroth element of the array. The code probably looks a little weird because the project is a little weird, but I think that is beside the point here. The SSL handshake completes. The issue is that instead of sending a certificate message on my behalf (in the handshake process), with the ASN.1 encoded certificate (MyLocalCertificate), the SslStream sends an SSL alert number 41 (no certificate) and then carries on. I know this from packet sniffing. After the handshake is completed, the SslStream marks IsAuthenticated as true, IsMutuallyAuthenticated as false, and its LocalCertificate member is null. I feel like I'm probably missing something pretty obvious here, so any ideas would be appreciated. I am a novice with SSL, and this project is off the beaten path, so I am kind of at a loss. P.S. 1: My ChooseLocalCertificate routine is called twice during the handshake, and returns a valid (as far as I can tell), non-null certificate both times. P.S. 2: SSLInOutStream is my own class, not a NetworkStream. Like I said, though, the handshake proceeds mostly normally, so I doubt this is the culprit... but who knows?

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  • Maintaining a Python web application: heavier vs lighter framework?

    - by Tiberiu Ana
    Five+ years from now, you are hired to support and extend a data-centric web application written in Python that hasn't been kept up to date. Would you rather prefer it was written in the current version of Django/Pylons at the time, using the available standard components, or kept minimal with something like CherryPy/web.py and a few library dependencies? Heavy framework Advantages: standard approach to application design and structure, as encouraged by framework; less application code to worry about. Disadvantages: requires learning the framework to understand how things work; broken things in old version of framework difficult to fix; upgrading to new version potentially difficult due to changing APIs; finding relevant documentation/help potentially difficult due to changing APIs. Light framework Advantages: most application code is directly "visible"; only needed features are implemented; architecture should be simpler to understand; less need to upgrade external dependencies; easier to upgrade external dependencies. Disadvantages: some reinventing the wheel; non-standard design and structure (with the associated unique issues and bugs). I will update the list with any helpful answers.

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  • Using datetime float representation as primary key

    - by devanalyst
    From my experience I have learn that using an surrogate INT data type column as primary key esp. an IDENTITY key column offers better performance than using GUID or char/varchar data type column as primary key. I try to use IDENTITY key as primary key wherever possible. But recently I came across a schema where the tables were horizontally partitioned and were managed via a Partitioned view. So the tables could not have an IDENTITY column since that would make the Partitioned View non updatable. One work around for this was to create a dummy 'keygenerator' table with an identity column to generate IDs for primary key. But this would mean having a 'keygenerator' table for each of the Partitioned View. My next thought was to use float as a primary key. The reason is the following key algorithm that I devised DECLARE @KEY FLOAT SET @KEY = CONVERT(FLOAT,GETDATE())/100000.0 SET @KEY = @EMP_ID + @KEY Heres how it works. CONVERT(FLOAT,GETDATE()) gives float representation of current datetime since internally all datetime are represented by SQL as a float value. CONVERT(FLOAT,GETDATE())/100000.0 converts the float representation into complete decimal value i.e. all digits are pushed to right side of ".". @KEY = @EMP_ID + @KEY adds the Employee ID which is an integer to this decimal value. The logic is that the Employee ID is guaranteed to be unique across sessions since an employee cannot connect to an application more than once at the same time. And for the same employee each time a key will be generated the current datetime will be unique. In all an unique key across all employee sessions and across time. So for Emp Ids 11 and 12, I have key values like 12.40046693321566357, 11.40046693542361111 But my concern whether float data type as primary key offer benefits compared to choosing GUID or char/varchar as primary keys. Also important thing is because of partitioning the float column is going to be part of a composite key.

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  • How to resolve user registration and activation email error in Django registration?

    - by user2476295
    So I was just trying to setup a basic user authentication in Django and downloaded a django registration app with templates. Now when I run the server at 127.0.0.1:8000/accounts/register/ I get a basic registration page, I fill in the details and when I click submit I get this error "NoReverseMatch at /accounts/register/" Error during template rendering In template Users/sudhasinha/mysite/mysite/registration/templates/registration/activation_email.txt, error at line 4 'url' requires a non-empty first argument. The syntax changed in Django 1.5, see the docs. 1 {% load i18n %} 2 {% trans "Activate account at" %} {{ site.name }}: 3 4 http://{{ site.domain }}{**% url registration_activate activation_key %**} 5 6 {% blocktrans %}Link is valid for {{ expiration_days }} days.{% endblocktrans %} 7 This is what my activation_email.txt looks like: {% load i18n %} {% trans "Activate account at" %} {{ site.name }}: http://{{ site.domain }}{% url registration_activate activation_key %} {% blocktrans %}Link is valid for {{ expiration_days }} days.{% endblocktrans %} And this is what my registration_form.html looks like: {% extends "base.html" %} {% load i18n %} {% block content %} <form method="post" action="."> {{ form.as_p }} <input type="submit" value="{% trans 'Submit' %}" /> </form> {% endblock %} I have very minimal experience with Django and would appreciate some help to resolve this error. My urls seem to be setup correctly but I will post it if needed. Also pardon my horrible formatting

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  • realloc() & ARC

    - by RynoB
    How would I be able to rewrite the the following utility class to get all the class string values for a specific type - using the objective-c runtime functions as shown below? The ARC documentation specifically states that realloc should be avoided and I also get the following compiler error on this this line: classList = realloc(classList, sizeof(Class) * numClasses); "Implicit conversion of a non-Objective-C pointer type 'void *' to '__unsafe_unretained Class *' is disallowed with ARC" The the below code is a reference to the original article which can be found here. + (NSArray *)classStringsForClassesOfType:(Class)filterType { int numClasses = 0, newNumClasses = objc_getClassList(NULL, 0); Class *classList = NULL; while (numClasses < newNumClasses) { numClasses = newNumClasses; classList = realloc(classList, sizeof(Class) * numClasses); newNumClasses = objc_getClassList(classList, numClasses); } NSMutableArray *classesArray = [NSMutableArray array]; for (int i = 0; i < numClasses; i++) { Class superClass = classList[i]; do { superClass = class_getSuperclass(superClass); if (superClass == filterType) { [classesArray addObject:NSStringFromClass(classList[i])]; break; } } while (superClass); } free(classList); return classesArray; } Your help will be much appreciated. Thanks

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  • UISegmentedControl Best Practice

    - by Neal L
    Hi all, I'm trying to work out the "best" way to use a UISegmentedControl for an iPhone application. I've read a few posts here on stackoverflow and seen a few people's ideas, but I can't quite sort out the best way to do this. The posts I'm referring to are: http://stackoverflow.com/questions/1559794/changing-views-from-uisegmentedcontrol and http://stackoverflow.com/questions/1047114/how-do-i-use-a-uisegmentedcontrol-to-switch-views It would seem that the options are: Add each of the views in IB and lay them out on top of each other then show/hide them Create each of the subviews separately in IB, then create a container in the main view to populate with the subview that you need Set up one really tall or really wide UIView and animate it left/right or up/down depending on the selected segment Use a UITabBarController to swap out the subviews - seems silly For tables, reload the table and in cellForRowAtIndex and populate the table from different data sources or sections based on the segment option selected (not the case for my app) So which approach is best for subview/non-table approaches? Which is the easiest to implement? Could you share some sample code to the approach? Thanks!

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  • Jquery $.get against ASP.NET MVC not working in Opera and Firefox

    - by codelove
    Let me first put the code snippets here. I am just using the ASP.NET MVC project Visual Studio creates out of the box. So I am just putting the snippets I added to it: Site.master's head section: <head runat="server"> <title><asp:ContentPlaceHolder ID="TitleContent" runat="server" /></title> <script src="../../Scripts/jquery-1.3.2.min.js" type="text/javascript"></script> <link href="../../Content/Site.css" rel="stylesheet" type="text/css" /> <script src="../../Scripts/test.js" type="text/javascript"></script> <script type="text/javascript">$(document).ready(ready);</script> </head> Content of test.js: function ready(){ $.get("/Home/TestAjax", ajaxResponse); } function ajaxResponse(data){ alert("got response from server: " + data); } Method in HomeController: public String TestAjax() { if (Request.IsAjaxRequest()) { return "Got ajax request!"; } else { return "Non-ajax request"; } } Now the problem I am seeing in Firefox 3.5.30729 (Firebug) is when the ajax request goes out, IIS 7 on the remote box sends Http 302 back, which does the redirect and forces another get request, but it is not asynchronous. Opera also doesn't work so I assume it is the same problem. However, above code works just fine in IE 8, Chrome, and Safari. On localhost all of the above browsers work as expected including Firefox and Opera -- they all receive "Got ajax request!" as the response from the server. Anybody have any ideas what's going on here and how to fix it? I am looking for a real solution or at least explanation as to what is going on and why.

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  • Generating all unique combinations for "drive ya nuts" puzzle

    - by Yuval A
    A while back I wrote a simple python program to brute-force the single solution for the drive ya nuts puzzle. The puzzle consists of 7 hexagons with the numbers 1-6 on them, and all pieces must be aligned so that each number is adjacent to the same number on the next piece. The puzzle has ~1.4G non-unique possibilities: you have 7! options to sort the pieces by order (for example, center=0, top=1, continuing in clockwise order...). After you sorted the pieces, you can rotate each piece in 6 ways (each piece is a hexagon), so you get 6**7 possible rotations for a given permutation of the 7 pieces. Totalling: 7!*(6**7)=~1.4G possibilities. The following python code generates these possible solutions: def rotations(p): for i in range(len(p)): yield p[i:] + p[:i] def permutations(l): if len(l)<=1: yield l else: for perm in permutations(l[1:]): for i in range(len(perm)+1): yield perm[:i] + l[0:1] + perm[i:] def constructs(l): for p in permutations(l): for c in product(*(rotations(x) for x in p)): yield c However, note that the puzzle has only ~0.2G unique possible solutions, as you must divide the total number of possibilities by 6 since each possible solution is equivalent to 5 other solutions (simply rotate the entire puzzle by 1/6 a turn). Is there a better way to generate only the unique possibilities for this puzzle?

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  • C# using consts in static classes

    - by NickLarsen
    I was plugging away on an open source project this past weekend when I ran into a bit of code that confused me to look up the usage in the C# specification. The code in questions is as follows: internal static class SomeStaticClass { private const int CommonlyUsedValue = 42; internal static string UseCommonlyUsedValue(...) { // some code value = CommonlyUsedValue + ...; return value.ToString(); } } I was caught off guard because this appears to be a non static field being used by a static function which some how compiled just fine in a static class! The specification states (§10.4): A constant-declaration may include a set of attributes (§17), a new modifier (§10.3.4), and a valid combination of the four access modifiers (§10.3.5). The attributes and modifiers apply to all of the members declared by the constant-declaration. Even though constants are considered static members, a constant-declaration neither requires nor allows a static modifier. It is an error for the same modifier to appear multiple times in a constant declaration. So now it makes a little more sense because constants are considered static members, but the rest of the sentence is a bit surprising to me. Why is it that a constant-declaration neither requires nor allows a static modifier? Admittedly I did not know the spec well enough for this to immediately make sense in the first place, but why was the decision made to not force constants to use the static modifier if they are considered constants? Looking at the last sentence in that paragraph, I cannot figure out if it is regarding the previous statement directly and there is some implicit static modifier on constants to begin with, or if it stands on its own as another rule for constants. Can anyone help me clear this up?

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  • Upgrade to Delphi 2010, or stick with Delphi 7 "forever"?

    - by tim11g
    I am an individual user of Delphi, starting back in the early Turbo Pascal days. I have quite a bit of code developed over the years, but I have never sold software commercially or used it for business. Historically, Borland supported the non-professional users with lower cost versions, but Embarcadero does not. As I consider upgrading to Delphi 2010, I am put off by the high price. Embarcadero is also trying to "encourage" upgrading by threatening to charge "new user" prices for upgrades after Dec 31st. I have several questions for the community to help me decide whether to upgrade. 1) I have read about difficulties updating existing code to support the unicode string types. I have no need for unicode strings, and I am happy with the string support in D7. Will I have to modify existing code and components just to re-compile under D2010? Or are there compiler options to allow backward compatibility if new string types are not required? 2) The main reason I'm considering upgrading is for IDE improvements, and to get access to new APIs added to Windows since 2002. Are there any Windows 7 APIs or capabilities that would be impossible to support from my programs compiled using using Delphi 7 (assuming appropriate JEDI API libraries, for example)? 3) Is there anything else about Delphi 2010 that is really compelling for someone who is primarily interested in Win32 apps, and not working with databases? I have read that D2010 is slow to load, and other versions between D7 and D2010 have had stability issues, and the help system was "broken". What is the biggest benefit to D2010?

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  • Calling web service using javascript error

    - by politrok
    Hi , I try to call webservice using json , when i call to web service without excepted parameters , its work , but when i'm try to send parameter , ive got an error : This is my code: function GetSynchronousJSONResponse(url, postData) { var xmlhttp = null; if (window.XMLHttpRequest) xmlhttp = new XMLHttpRequest(); else if (window.ActiveXObject) { if (new ActiveXObject("Microsoft.XMLHTTP")) xmlhttp = new ActiveXObject("Microsoft.XMLHTTP"); else xmlhttp = new ActiveXObject("Msxml2.XMLHTTP"); } url = url + "?rnd=" + Math.random(); // to be ensure non-cached version xmlhttp.open("POST", url, false); xmlhttp.setRequestHeader("Content-Type", "application/json; charset=utf-8"); xmlhttp.send(postData); var responseText = xmlhttp.responseText; return responseText; } function Test() { var result = GetSynchronousJSONResponse('http://localhost:1517/Mysite/Myservice.asmx/myProc', '{"MyParam":"' + 'test' + '"}'); result = eval('(' + result + ')'); alert(result.d); } This is the error : System.InvalidOperationException: Request format is invalid: application/json; charset=utf-8. at System.Web.Services.Protocols.HttpServerProtocol.ReadParameters() at System.Web.Services.Protocols.WebServiceHandler.CoreProcessRequest What is wrong ? Thanks in advance .

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  • Multiple undo managers for a text view

    - by Rui Pacheco
    Hi, I've a text view that gets its content from an attributed string stored in a model object. I list several of these model objects in a drawer and when the user clicks on one the text view swaps its content. I now need to also swap the undo manager for the text view. I initialise an undo manager on my model object and use undoManagerForTextView to return it to the text view, but something's not quite right. Strategically placed logging statements show me that everything's working as planned: on startup a new model object is initialised correctly and a non-null undo manager is always pulled by the text view. But when it comes to actually doing undo, I just can't get the behaviour I want. I open a window, type something and press cmd+z, and undo works. I open a window, type something, select a new model on the table, type something, go back to the first model and try to undo and all I get is a beep. Something on the documentation made me raise an eyebrow, as it would mean that I can't have undo with several model objects: The default undo and redo behavior applies to text fields and text in cells as long as the field or cell is the first responder (that is, the focus of keyboard actions). Once the insertion point leaves the field or cell, prior operations cannot be undone.

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  • Archive log transfer from Oracle 9i to Oracle 10g

    - by Jamie Love
    Hi all, I have a situation where I need to transfer Oracle 9i archive logs to an Oracle 10g database, from where they are to be mined by a log-miner and then used by an Oracle streams capture/apply processes. (Oracle 9 archive logs can be read by the Oracle 10 logminer - I can manually copy the archive logs across, manually register them and have them mined, captured then applied). The difficulty is that the way Oracle does archive log transfer changed quite a bit between 9i and 10g and setting up the 9i database to transfer to the remote machine like so: log_archive_dest_state_2 = enable log_archive_dest_2 = "service=OTHERMACHINE arch optional" no longer works. I get this in the 9i logs: *** 2009-05-22 04:03:44.149 RFS network connection lost at host 'OTHERMACHINE' Error 3113 attaching RFS server to standby instance at host 'OTHERMACHINE' Error 3113 attaching to destination LOG_ARCHIVE_DEST_2 standby host 'OTHERMACHINE' Heartbeat failed to connect to standby 'OTHERMACHINE'. Error is 3113. *** 2009-05-22 04:03:44.150 kcrrfail: dest:2 err:3113 force:0 ORA-03113: end-of-file on communication channel And in the 10g log I get: Fri May 22 04:07:42 2009 WARNING: inbound connection timed out (ORA-3136) My question is: Does anyone know how I could configure my 9i or 10g server such that the 10g server will accept the 9i connection in such a way that I can transfer the 9i archive logs to the 10g server. It would be a bonus if the archive logs would be automatically registered in the 10g server. Note I have not set up a full DataGuard configuration here and the 10g database is not a secondary server. Thanks for any suggestions. Edit Note that I can log on to the 10g server from the 9i server via sqlplus, so connectivity is not the problem Edit 2 After a large amount of time searching for a solution, I've finally decided that such a mechanism doesn't work, and that a non-Oracle method of transferring archive logs from 9i to 10g will need to be used (e.g. rsync).

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  • What's with the love of dynamic Languages

    - by Kibbee
    It seems that everybody is jumping on the dynamic, non-compiled bandwagon lately. I've mostly only worked in compiled, static typed languages (C, Java, .Net). The experience I have with dynamic languages is stuff like ASP (Vb Script), JavaScript, and PHP. Using these technologies has left a bad taste in my mouth when thinking about dynamic languages. Things that usually would have been caught by the compiler such as misspelled variable names and assigning an value of the wrong type to a variable don't occur until runtime. And even then, you may not notice an error, as it just creates a new variable, and assigns some default value. I've also never seen intellisense work well in a dynamic language, since, well, variables don't have any explicit type. What I want to know is, what people find so appealing about dynamic languages? What are the main advantages in terms of things that dynamic languages allow you to do that can't be done, or are difficult to do in compiled languages. It seems to me that we decided a long time ago, that things like uncompiled asp pages throwing runtime exceptions was a bad idea. Why is there is a resurgence of this type of code? And why does it seem to me at least, that Ruby on Rails doesn't really look like anything you couldn't have done with ASP 10 years ago?

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  • Simple Select Statement on MySQL Database Hanging

    - by AlishahNovin
    I have a very simple sql select statement on a very large table, that is non-normalized. (Not my design at all, I'm just trying to optimize while simultaneously trying to convince the owners of a redesign) Basically, the statement is like this: SELECT FirstName, LastName, FullName, State FROM Activity Where (FirstName=@name OR LastName=@name OR FullName=@name) AND State=@state; Now, FirstName, LastName, FullName and State are all indexed as BTrees, but without prefix - the whole column is indexed. State column is a 2 letter state code. What I'm finding is this: When @name = 'John Smith', and @state = '%' the search is really fast and yields results immediately. When @name = 'John Smith', and @state = 'FL' the search takes 5 minutes (and usually this means the web service times out...) When I remove the FirstName and LastName comparisons, and only use the FullName and State, both cases above work very quickly. When I replace FirstName, LastName, FullName, and State searches, but use LIKE for each search, it works fast for @name='John Smith%' and @state='%', but slow for @name='John Smith%' and @state='FL' When I search against 'John Sm%' and @state='FL' the search finds results immediately When I search against 'John Smi%' and @state='FL' the search takes 5 minutes. Now, just to reiterate - the table is not normalized. The John Smith appears many many times, as do many other users, because there is no reference to some form of users/people table. I'm not sure how many times a single user may appear, but the table itself has 90 Million records. Again, not my design... What I'm wondering is - though there are many many problems with this design, what is causing this specific problem. My guess is that the index trees are just too large that it just takes a very long time traversing the them. (FirstName, LastName, FullName) Anyway, I appreciate anyone's help with this. Like I said, I'm working on convincing them of a redesign, but in the meantime, if I someone could help me figure out what the exact problem is, that'd be fantastic.

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  • In-document schema declarations and lxml

    - by shylent
    As per the official documentation of lxml, if one wants to validate a xml document against a xml schema document, one has to construct the XMLSchema object (basically, parse the schema document) construct the XMLParser, passing the XMLSchema object as its schema argument parse the actual xml document (instance document) using the constructed parser There can be variations, but the essense is pretty much the same no matter how you do it, - the schema is specified 'externally' (as opposed to specifying it inside the actual xml document). If you follow this procedure, the validation occurs, sure enough, but if I understand it correctly, that completely ignores the whole idea of the schemaLocation and noNamespaceSchemaLocation attributes from xsi. This introduces a whole bunch of limitations, starting with the fact, that you have to deal with instance<-schema relation all by yourself (either store it externally or write some hack to retrieve the schema location from the root element of the instance document), you can not validate the document using multiple schemata (say, when each schema governs its own namespace) and so on. So the question is: maybe I am missing something completely trivial or doing it wrong? Or are my statements about lxml's limitations regarding schema validation true? To recap, I'd like to be able to: have the parser use the schema location declarations in the instance document at parse/validation time use multiple schemata to validate a xml document declare schema locations on non-root elements (not of extreme importance) Maybe I should look for a different library? Although, that'd be a real shame, - lxml is a de-facto xml processing library for python and is regarded by everyone as the best one in terms of performace/features/convenience (and rightfully so, to a certain extent)

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  • iPhone app: How to implement in-app purchased game levels

    - by Wonderflonium
    So, I understand that it's possible to set up in-app purchases for iPhone apps to purchase non-consumables like game levels. I understand the logic behind the purchase part, but what I don't understand is, how can I deliver the new game level. For example: I build an app that contains the first level and they purchase additional levels. Is it better to build all the other levels into the app and whenever they purchase the app, it unlocks it with a plist entry or something? That doesn't seem very update-able to me. Every time I come up with a new level, I'd have to update the app. So, what I don't understand then, is what is how do I package up a level and download it as a separate entity that can accessed by the game? Would the level just be some XML with images in a ZIP folder or something? How does the level get added to the game? What are best practices for this type of thing? I Googled and have found NOTHING about this. I'm a little bit confused by the concept and any help would be appreciated. I'm not looking for someone to write the game for me, I just need pointed in the right direction so I can develop it on my own.

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  • Workflow engine BPMN, Drools, etc or ESB?

    - by Tom
    We currently have an application that is based on an in-house developed workflow engine with YAML based DSL. We are looking to move parts of it to Java. I have discovered a number of java solutions like Intalio, JBPM, Drools Expert, Drools Flow etc. They appear to be aimed at businesses where the business analyst creates the workflows using a graphical editor and submits them to the workflow engine. They seem geared towards ease of use for non-technical people rather than for developers with a focus on human interaction. The workflows tend to look like. Discover-a-file -\ -> join -> process-file -> move-file -> register-file Discover-some-metadata -/ If any step fails we need to retry it X times. We also need to be able to stop the system and be able to restart it and have it continue from where it was (durable). Some of our workflows can be defined by a set of goals we need to achieve so Jess's backwards rule chaining sounds interesting but it is not open source. It might be that what we are after is a Finite State Machine engine or just an Enterprise Service Bus and do everything as JMS queues. Is there a good open source workflow engine that is both standards-based but also geared towards developers. We don't particular want to use a graphical workflow designer or write reams of XML and it should ideally be in Java or language agnostic (makes REST/Soap calls to external services). Thanks, Tom

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  • Help with dynamic-wind and call/cc

    - by josh
    I am having some trouble understanding the behavior of the following Scheme program: (define c (dynamic-wind (lambda () (display 'IN)(newline)) (lambda () (call/cc (lambda (k) (display 'X)(newline) k))) (lambda () (display 'OUT)(newline)))) As I understand, c will be bound to the continution created right before "(display 'X)". But using c seems to modify itself! The define above prints (as I expected) IN, X and OUT: IN X OUT And it is a procedure: #;2> c #<procedure (a9869 . results1678)> Now, I would expect that when it is called again, X would be printed, and it is not! #;3> (c) IN OUT And now c is not a procedure anymore, and a second invokation of c won't work! #;4> c ;; the REPL doesn't answer this, so there are no values returned #;5> (c) Error: call of non-procedure: #<unspecified> Call history: <syntax> (c) <eval> (c) <-- I was expecting that each invokation to (c) would do the same thing -- print IN, X, and OUT. What am I missing?

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  • x86 CMP Instruction Difference

    - by Pindatjuh
    Question What is the (non-trivial) difference between the following two x86 instructions? 39 /r CMP r/m32,r32 Compare r32 with r/m32 3B /r CMP r32,r/m32 Compare r/m32 with r32 Background I'm building a Java assembler, which will be used by my compiler's intermediate language to produce Windows-32 executables. Currently I have following code: final ModelBase mb = new ModelBase(); // create new memory model mb.addCode(new Compare(Register.ECX, Register.EAX)); // add code mb.addCode(new Compare(Register.EAX, Register.ECX)); // add code final FileOutputStream fos = new FileOutputStream(new File("test.exe")); mb.writeToFile(fos); fos.close(); To output a valid executable file, which contains two CMP instruction in a TEXT-section. The executable outputted to "text.exe" will do nothing interesting, but that's not the point. The class Compare is a wrapper around the CMP instruction. The above code produces (inspecting with OllyDbg): Address Hex dump Command 0040101F |. 3BC8 CMP ECX,EAX 00401021 |. 3BC1 CMP EAX,ECX The difference is subtle: if I use the 39 byte-opcode: Address Hex dump Command 0040101F |. 39C1 CMP ECX,EAX 00401021 |. 39C8 CMP EAX,ECX Which makes me wonder about their synonymity and why this even exists.

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  • How to convert an InputStream to a DataHandler?

    - by pcorey
    I'm working on a java web application in which files will be stored in a database. Originally we retrieved files already in the DB by simply calling getBytes on our result set: byte[] bytes = resultSet.getBytes(1); ... This byte array was then converted into a DataHandler using the obvious constructor: dataHandler=new DataHandler(bytes,"application/octet-stream"); This worked great until we started trying to store and retrieve larger files. Dumping the entire file contents into a byte array and then building a DataHandler out of that simply requires too much memory. My immediate idea is to retrieve a stream of the data in the database with getBinaryStream and somehow convert that InputStream into a DataHandler in a memory-efficient way. Unfortunately it doesn't seem like there's a direct way to convert an InputStream into a DataHandler. Another idea I've been playing with is reading chunks of data from the InputStream and writing them to the OutputStream of the DataHandler. But... I can't find a way to create an "empty" DataHandler that returns a non-null OutputStream when I call getOutputStream... Has anyone done this? I'd appreciate any help you can give me or leads in the right direction.

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  • Minimal-change algorithm which maximises 'swapping'

    - by Kim Bastin
    This is a question on combinatorics from a non-mathematician, so please try to bear with me! Given an array of n distinct characters, I want to generate subsets of k characters in a minimal-change order, i.e. an order in which generation n+1 contains exactly one character that was not in generation n. That's not too hard in itself. However, I also want to maximise the number of cases in which the character that is swapped out in generation n+1 is the same character that was swapped in in generation n. To illustrate, for n=7, k=3: abc abd abe* abf* abg* afg aeg* adg* acg* acd ace* acf* aef adf* ade bde bdf bef bcf* bce bcd* bcg* bdg beg* bfg* cfg ceg* cdg* cde cdf* cef def deg dfg efg The asterisked strings indicate the case I want to maximise; e.g. the e that is new in generation 3, abe, replaces a d that was new in generation 2, abd. It doesn't seem possible to have this happen in every generation, but I want it to happen as often as possible. Typical array sizes that I use are 20-30 and subset sizes around 5-8. I'm using an odd language, Icon (or actually its derivative Unicon), so I don't expect anyone to post code that I can used directly. But I will be grateful for answers or hints in pseudo-code, and will do my best to translate C etc. Also, I have noticed that problems of this kind are often discussed in terms of arrays of integers, and I can certainly apply solutions posted in such terms to my own problem. Thanks Kim Bastin

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  • SQLiteDataAdapter Fill exception C# ADO.NET

    - by Lirik
    I'm trying to use the OleDb CSV parser to load some data from a CSV file and insert it into a SQLite database, but I get an exception with the OleDbAdapter.Fill method and it's frustrating: An unhandled exception of type 'System.Data.ConstraintException' occurred in System.Data.dll Additional information: Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign-key constraints. Here is the source code: public void InsertData(String csvFileName, String tableName) { String dir = Path.GetDirectoryName(csvFileName); String name = Path.GetFileName(csvFileName); using (OleDbConnection conn = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + dir + @";Extended Properties=""Text;HDR=No;FMT=Delimited""")) { conn.Open(); using (OleDbDataAdapter adapter = new OleDbDataAdapter("SELECT * FROM " + name, conn)) { QuoteDataSet ds = new QuoteDataSet(); adapter.Fill(ds, tableName); // <-- Exception here InsertData(ds, tableName); // <-- Inserts the data into the my SQLite db } } } class Program { static void Main(string[] args) { SQLiteDatabase target = new SQLiteDatabase(); string csvFileName = "D:\\Innovations\\Finch\\dev\\DataFeed\\YahooTagsInfo.csv"; string tableName = "Tags"; target.InsertData(csvFileName, tableName); Console.ReadKey(); } } The "YahooTagsInfo.csv" file looks like this: tagId,tagName,description,colName,dataType,realTime 1,s,Symbol,symbol,VARCHAR,FALSE 2,c8,After Hours Change,afterhours,DOUBLE,TRUE 3,g3,Annualized Gain,annualizedGain,DOUBLE,FALSE 4,a,Ask,ask,DOUBLE,FALSE 5,a5,Ask Size,askSize,DOUBLE,FALSE 6,a2,Average Daily Volume,avgDailyVolume,DOUBLE,FALSE 7,b,Bid,bid,DOUBLE,FALSE 8,b6,Bid Size,bidSize,DOUBLE,FALSE 9,b4,Book Value,bookValue,DOUBLE,FALSE I've tried the following: Removing the first line in the CSV file so it doesn't confuse it for real data. Changing the TRUE/FALSE realTime flag to 1/0. I've tried 1 and 2 together (i.e. removed the first line and changed the flag). None of these things helped... One constraint is that the tagId is supposed to be unique. Here is what the table look like in design view: Can anybody help me figure out what is the problem here?

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  • Pros & Cons of Google App Engine

    - by Rishi
    Pros & Cons of Google App Engine [An Updated List 21st Aug 09] Help me Compile a List of all the Advantages & Disadvantages of Building an Application on the Google App Engine Pros: 1) No Need to buy Servers or Server Space (no maintenance). 2) Makes solving the problem of scaling much easier. Cons: 1) Locked into Google App Engine ?? 2)Developers have read-only access to the filesystem on App Engine. 3)App Engine can only execute code called from an HTTP request (except for scheduled background tasks). 4)Users may upload arbitrary Python modules, but only if they are pure-Python; C and Pyrex modules are not supported. 5)App Engine limits the maximum rows returned from an entity get to 1000 rows per Datastore call. 6)Java applications may only use a subset (The JRE Class White List) of the classes from the JRE standard edition. 7)Java applications cannot create new threads. Known Issues!! http://code.google.com/p/googleappengine/issues/list Hard limits Apps per developer - 10 Time per request - 30 sec Files per app - 3,000 HTTP response size - 10 MB Datastore item size - 1 MB Application code size - 150 MB Pro or Con? App Engine's infrastructure removes many of the system administration and development challenges of building applications to scale to millions of hits. Google handles deploying code to a cluster, monitoring, failover, and launching application instances as necessary. While other services let users install and configure nearly any *NIX compatible software, App Engine requires developers to use Python or Java as the programming language and a limited set of APIs. Current APIs allow storing and retrieving data from a BigTable non-relational database; making HTTP requests; sending e-mail; manipulating images; and caching. Most existing Web applications can't run on App Engine without modification, because they require a relational database.

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