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• Learning Basic Mathematics

  - by NeedsToKnow

  I'm going to just come out and say it. I'm 20 and can't do maths. Two years ago I passed the end-of-high-school mathematics exam (but not at school), and did pretty well. Since then, I haven't done a scrap of mathematics. I wondered just how bad I had gotten, so I was looking at some simple algebra problems. You know, the kind you learn halfway through highschool. 5(-3x - 2) - (x - 3) = -4(4x + 5) + 13 Couldn't do them. I've got half a year left until I start a Computer Science undergraduate degree. I love designing and creating programs, and I remember I loved mathematics back when I did it. Basically, I've had a pretty bad education, but I want to be knowledgable in these areas. I was thinking of buying some high school textbooks and reading them, but I'm not sure this is the right way to go. I need to start off at some basic level and work towards a greater understanding. My question is: What should I study, how should I study, and what books can you recommend? Thanks!

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• Fast, easy, and secure method to perform DB actions with GET

  - by rob - not a robber

  Hey All, Sort of a methods/best practices question here that I am sure has been addressed, yet I can't find a solution based on the vague search terms I enter. I know starting off the question with "Fast and easy" will probably draw out a few sighs, so my apologies. Here is the deal. I have a logged in area where an ADMIN can do a whole host of POST operations to input data relating to their profile. The way I have data structured is pretty distinct and well segmented in most tables as it relates to the ID of the admin. Now, I have a table where I dump one type of data into and differentiate this data by assigning the ADMIN's unique ID to each record. In other words, all ADMINs have this one type of data writing to this table. I just differentiate by the ADMIN ID with each record. I was planning on letting the ADMIN remove these records by clicking on a link with a query string - obviously using GET. Obviously, the query structure is in the link so any logged in admin could then exploit the URL and delete a competitor's records. Is the only way to safely do this through POST or should I pass through the session info that includes password and validate it against the ADMIN ID that is requesting the delete? This is obviously much more work for me. As they said in the auto repair biz I used to work in... there are 3 ways to do a job: Fast, Good, and Cheap. You can only have two at a time. Fast and cheap will not be good. Good and cheap will not have fast turnaround. Fast and good will NOT be cheap. haha I guess that applies here... can never have Fast, Easy and Secure all at once ;) Thanks in advance...

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• Named previously unnamed branch

  - by Jab

  It seems naming a previously unnamed branch doesn't really work out. It creates a nasty multiple heads problem that I can't find a solution for. Here is the workflow... UserA starts working on feature that they expect to be small, so they just start working(off the default branch). The change turns out to be a large project and will need multiple contributors. So UserA issues... hg branch "Feature1" and continues working, committing locally s needed. UserA then pulls down the changes from the central repo so he can push. At this point, why does hg heads return 3 heads? It shows 2 for default and 1 for Feature1. The first head for default is the latest change by another user on the branch(irrelevant). The second default head is the commit prior to the hg branch "Feature1" commit. The central repository has rules enforced so that only 1 head per branch is allowed, so forcing a push isn't an option. The repo doesn't want multiple heads on the default branch. UserA should be able to push these changes so that other users can see the Feature1 branch and help out. I can't seem to find a way to "correct" this. I don't think I can re-write the branch of the initial commits for the feature, before it was a named branch. I know the initial changes before the named branch are technically on the default branch, but does that mean they will be heads until that Feature1 branch is merged?

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• A potentially dangerous Request.Form value was detected: Dealing with these errors proactively, or a

  - by Albert

  I'm noticing this error more and more in my error logs. I've read through the questions here talking about this error, but they don't address what I would like to do (see below). I'm considering three options, in the order of preference: 1) When submitting a form (I use formviews almost exclusively, if that helps), if potentially dangerous characters are detected, automatically strip them out and submit. 2) When submitting a form, if potentially dangerous characters are detected, alert the user and let them fix it before trying again. 3) After the exception is generated, deal with it and alert the user. I'm hoping one of the first two options might be able to do somewhat globally...I know for the 3rd I'd have to alter a TON of Try-Catch blocks I already have in place. Doable, but labor intensive. I'd rather be proactive about it if at all possible and avoid the exception all together. Perhaps one approach to #1 would be to write a block of code that could loop through all text entry fields in a formview, during the insert/update event, and strip the characters out. I'm ok with that, but I'd rather not have to heavily alter all my Insert/Update events to accomplish this. Or maybe I just create a different class to do the text checking/deleting, and only insert 1 line of code in each Insert/Update event. If anyone can come up with some example code of any of these approaches that would be a help. Thanks for any ideas or information. I'm definitely open to other solutions too; these are only the 3 that came to mind. I can say that I don't want to turn request validation off though.

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• Splitting 25mb .txt file into smaller files using text delimiter

  - by user574141

  Regards, SO I am new to python and Perl. I have been trying to solve a simple problem and getting tied in knots with syntax. I hope someone has the time and patience to help. I have a 25mb file in ".txt" format which contains news-wire articles going back to 1970. Each news story is concatenated to the next, with only the "Copyright" statement to delimit. Each news story starts with "Item XX of XXX DOCUMENTS". There are certain metadata that are repeated throughout, I will use these for tagging later on. I wish to split this 25mb file into separate .txt files, each containing one news story (i.e. the text between "DOCUMENTS" and "Copyright", saving each with a different name (obviously). I am trying to 1 ) open the file... 2) iterate over lines in the file checking for the eof delimiter, and if it is not present writing the line to a list 3)write that list to a seperate small file. I'm having big problems with changing filenames using the counter, and how do I make Python start from where I left off, is the "seek" function appropriate? so far I have been trying this approach, completely unsuccessfully: myfile = open ("myfile.txt", 'r') filenumber = 0 for line in myfile.readline(): filenumber += 1 w=0 while myfile.readline() != '\s+DOCUMENTS\s*\n' ### read my line into a list mysmallfile()['w'] = [myfile.readline()] w += 1 output = open('C:\\Users\\dunner7\\Documents\###how do I change the filename each iteration???', 'w') output.writelines(mysmallfile) ###go back to start. Thank you for your time and patience. RD

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• Batch File to Delete Folders

  - by Homebrew

  I found some code to delete folders, in this case deleting all but 'n' # of folders. I created 10 test folders, plus 1 that was already there. I want to delete all but 4. The code works, it leaves 4 of my test folders, except that it also leaves the other folder. Is there some attribute of the other folder that's getting checked in the batch file that's stopping it from getting deleted ? It was created through a job a couple of weeks ago. Here's the code I stole (but don't really understand the details): rem DOS - Delete Folders if # folders > n @Echo Off :: User Variables :: Set this to the number of folders you want to keep Set _NumtoKeep=4 :: Set this to the folder that contains the folders to check and delete Set _Path=C:\MyFolder_Temp\FolderTest If Exist "%temp%\tf}1{" Del "%temp%\tf}1{" PushD %_Path% Set _s=%_NumtoKeep% If %_NumtoKeep%==1 set _s=single For /F "tokens=* skip=%_NumtoKeep%" %%I In ('dir "%_Path%" /AD /B /O-D /TW') Do ( If Exist "%temp%\tf}1{" ( Echo %%I:%%~fI >>"%temp%\tf}1{" ) Else ( Echo.>"%temp%\tf}1{" Echo Do you wish to delete the following folders?>>"%temp%\tf}1{" Echo Date Name>>"%temp%\tf}1{" Echo %%I:%%~fI >>"%temp%\tf}1{" )) PopD If Not Exist "%temp%\tf}1{" Echo No Folders Found to delete & Goto _Done Type "%temp%\tf}1{" | More Set _rdflag= /q Goto _Removeold Set _rdflag= :_Removeold For /F "tokens=1* skip=3 Delims=:" %%I In ('type "%temp%\tf}1{"') Do ( If "%_rdflag%"=="" Echo Deleting rd /s%_rdflag% "%%J") :_Done If Exist "%temp%\tf}1{" Del "%temp%\tf}1{"

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• What are the lengths/limits C preprocessor as a language creation tool? Where can I learn more about

  - by Weston C

  In his FAQ @ http://www2.research.att.com/~bs/bs_faq.html#bootstrapping, Bjarne Stroustrup says: To build [Cfront, the first C++ compiler], I first used C to write a "C with Classes"-to-C preprocessor. "C with Classes" was a C dialect that became the immediate ancestor to C++... I then wrote the first version of Cfront in "C with Classes". When I read this, it piqued my interest in the C preprocessor. I'd seen its macro capabilities as suitable for simplifying common expressions but hadn't thought about its ability to significantly add to syntax and semantics on the level that I imagine bringing classes to C took. So now I have a couple of questions on my mind: 1) Are there other examples of this approach to bootstrapping a language off of C? 2) Is the source to Stroustrup's original work available anywhere? 3) Where could I learn more about the specifics of utilizing this technique? 4) What are the lengths/limits of that approach? Could one, say, create a set of preprocessor macros that let someone write in something significantly Lisp/Scheme like?

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• NSTimer as a timeout mechanism

  - by alexantd

  I'm pretty sure this is really simple, and I'm just missing something obvious. I have an app that needs to download data from a web service for display in a UITableView, and I want to display a UIAlertView if the operation takes more than X seconds to complete. So this is what I've got (simplified for brevity): MyViewController.h @interface MyViewController : UIViewController <UITableViewDelegate, UITableViewDataSource> { NSTimer *timer; } @property (nonatomic, retain) NSTimer *timer; MyViewController.m @implementation MyViewController @synthesize timer; - (void)viewDidLoad { timer = [NSTimer scheduledTimerWithTimeInterval:20 target:self selector:@selector(initializationTimedOut:) userInfo:nil repeats:NO]; [self doSomethingThatTakesALongTime]; [timer invalidate]; } - (void)doSomethingThatTakesALongTime { sleep(30); // for testing only // web service calls etc. go here } - (void)initializationTimedOut:(NSTimer *)theTimer { // show the alert view } My problem is that I'm expecting the [self doSomethingThatTakesALongTime] call to block while the timer keeps counting, and I'm thinking that if it finishes before the timer is done counting down, it will return control of the thread to viewDidLoad where [timer invalidate] will proceed to cancel the timer. Obviously my understanding of how timers/threads work is flawed here because the way the code is written, the timer never goes off. However, if I remove the [timer invalidate], it does.

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• Common Lisp condition system for transfer of control

  - by Ken

  I'll admit right up front that the following is a pretty terrible description of what I want to do. Apologies in advance. Please ask questions to help me explain. :-) I've written ETLs in other languages that consist of individual operations that look something like: // in class CountOperation IEnumerable<Row> Execute(IEnumerable<Row> rows) { var count = 0; foreach (var row in rows) { row["record number"] = count++; yield return row; } } Then you string a number of these operations together, and call The Dispatcher, which is responsible for calling Operations and pushing data between them. I'm trying to do something similar in Common Lisp, and I want to use the same basic structure, i.e., each operation is defined like a normal function that inputs a list and outputs a list, but lazily. I can define-condition a condition (have-value) to use for yield-like behavior, and I can run it in a single loop, and it works great. I'm defining the operations the same way, looping through the inputs: (defun count-records (rows) (loop for count from 0 for row in rows do (signal 'have-value :value `(:count ,count @,row)))) The trouble is if I want to string together several operations, and run them. My first attempt at writing a dispatcher for these looks something like: (let ((next-op ...)) ;; pick an op from the set of all ops (loop (handler-bind ((have-value (...))) ;; records output from operation (setq next-op ...) ;; pick a new next-op (call next-op))) But restarts have only dynamic extent: each operation will have the same restart names. The restart isn't a Lisp object I can store, to store the state of a function: it's something you call by name (symbol) inside the handler block, not a continuation you can store for later use. Is it possible to do something like I want here? Or am I better off just making each operation function explicitly look at its input queue, and explicitly place values on the output queue?

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• Programmatic Text Wrapping in TextView

  - by Andrew

  I'm working on a custom widget for my application to replicate the look of a Preference button for layouts. The issue is the 'summary' text wont wrap when it hits the right wall of the view. One of the goals I'm trying to keep is that this widget is completely made from java with no xml attributes. here's what the widget looks like at the moment: http://dl.dropbox.com/u/56017670/Screenshot_2012-09-05-17-22-45.png notice that the middle two don't wrap the text but the text obviously runs right off the edge of the widget below is the code I'm using to create the text view. public void setSummary(String summary) { if (!TextUtils.isEmpty(summary)) { if (mSummaryView == null) { mSummaryView = new TextView(mContext); mSummaryView.setTextSize(14); mSummaryView.setTextColor(mContext.getResources().getColor( android.R.color.tertiary_text_dark)); addView(mSummaryView); } mSummaryView.setText(summary); mSummaryView.setVisibility(View.VISIBLE); } else { if (mSummaryView != null) { mSummaryView.setVisibility(View.GONE); } } mSummaryText = summary; } and here is the code I'm using to layout mSummaryView mSummaryView.layout( mPreferencePadding + mIconWidth, centerVertical + (mCombinedTextHeight / 2) - mSummaryHeight, width - mPreferencePadding, centerVertical + (mCombinedTextHeight / 2)); I've tried to add mSummaryView.setSingleLine(false); along with quite a few other tricks but they all ended in the same way.

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• Return latitude/longitude based on entered address

  - by Don

  I'm building a php based application for a client to enter in addresses for their customers' buildings. They'd like the ability to view the location on a map (either as individuals or grouped in a city search). What I'm trying to accomplish is a lookup once the address is entered into a form that populates the database, so after they enter in the addresss, city, state, zip (these are all US locations) they could click a "get lat/long info" link/button that would check to make sure the data is complete, then would lookup the address and return the latitude/longitude into the appropriate form fields. Then the form could be submitted to store the info, and I could later just pull the lat/long when plotting on a map. 1) Does this make sense, or would I be better off just doing the lookup when it's time to plot it? 2) Does anyone have any pointers to solve this problem? I've seen some of the Google/Yahoo API's but it looks like this is more based on the plotting a point part. I may be able to modify it to suit my needs, but I'm just trying to cut some research time posting here with the hopes one of you may have a more direct route. I'll RTFM if I have to... Thanks, D.

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• Nhibernate beginner - asking for directions

  - by George

  Hello guys. I'm starting off with NHibernate now and I still don't have a testable environment. I would like to know from you, experienced fellows if there is a problem to map IList to an Set in .hbm file. Like this: //c# IList<TrechoItem> trechos_item; <!-- xml .hbm --> <set name="TrechosItem" table="trecho_item" lazy="true" inverse="true" fetch="select"> <key column="id_item"/> <one-to-many class="TrechoItem"/> </set> Or, in this: IList<Autor> Autores; <set name="Autores" lazy="true" table="item_possui_autor"> <key column="id_item"/> <many-to-many class="Autor" column="id_autor"/> </set> Is this possible? Or am I doing the wrong thing? I tried using and but these did not gave me all the options in . Thanks in advanced

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• Refactoring or Rewriting Monolithic PHP Spaghetti Codebase

  - by nategood

  I've inherited a really poorly designed PHP spaghetti code project. It's been gaining a good bit of traffic recently and is starting to have performance issues on top of the poor monolithic code base. Its maxing out performance on a chunky 16GB dedicated machine when it really shouldn't be. I'm planning on doing some performance tweaks right off the bat to help the performance issue, but this still won't really help the horrible code base. The team is small but expecting to grow very soon. I've read Joel's article on the troubles of doing a complete rewrite and see the concerns. But how bad does the code base have to be before you consider a rewrite? There is PHP handling logic interjected into what one would usually consider a "view". Even worse, in some places SQL statements are in these same files! The only real separation of presentation and logic are a few PHP scripts that serve as function libraries. These scripts do most of the ORM stuff... if you can even call it that. Trying to slowly refractor this seems like a nightmare. Open to your thoughts and opinions... however not interested in hearing, "Run away, Run away!".

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• How do I perform a flip and grow animation like in iPhoto 09?

  - by Austin

  I'm developing a Cocoa application and want to be able to click a button in one of the views in my NSCollectionView and have a details view flip open and position to the middle of the screen like it does in iPhoto 09 when you click the "i" in the bottom-right hand corner of a photo. The photo "flips" and grows, centered on the window to reveal details about the photo. I'm guessing they're using Core Animation to achieve this. I've been looking at the Lemur Flip example, but when I try to modify it to add repositioning code to the animation, it throws off the flip. Here is the positioning code I've added to the - (IBAction)flip:(id)sender; code of LemurFlip: ... [CATransaction begin]; { NSSize supersize = contentView.frame.size; // Size of window content view NSSize subsize = frontView.frame.size; // Size of view we're flipping out if(!frontView.isHidden) { // Move views to middle of the window [[backView animator] setFrameOrigin:NSMakePoint((supersize.width / 2) - (subsize.width / 2), (supersize.height / 2) - (subsize.height / 2))]; [[frontView animator] setFrameOrigin:NSMakePoint((supersize.width / 2) - (subsize.width / 2), (supersize.height / 2) - (subsize.height / 2))]; } else { // Return views to point of origin [[backView animator] setFrameOrigin:NSMakePoint(0, 0)]; [[frontView animator] setFrameOrigin:NSMakePoint(0, 0)]; } [hiddenLayer addAnimation:[self _flipAnimationWithDuration:flipDuration isFront:NO] forKey:@"flipGroup"]; [visibleLayer addAnimation:[self _flipAnimationWithDuration:flipDuration isFront:YES] forKey:@"flipGroup"]; } [CATransaction commit]; ... Is there a good example of how to do this or some rules for combining these sort of animations?

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• How do I update the UI during an event using ASP.NET?

  - by Phil Hale

  I'm a bit stuck with a problem. I feel like the solution should be fairly straight forward but I'm completely out of ideas for some reason. Here's the problem. I've got a user control with a couple of buttons. Think of them as 'On' and 'Off'. When either button is clicked an async method is called. If the method is successful an event is fired. Within the event I want to update the enabled property of the two buttons so that only a single button is clickable at any one time. The problem is that any changes I make to the properties are not shown on screen because the postback is already complete. I tried wrapping the buttons in an UpdatePanel but I get an "Update method can only be called on UpdatePanel with ID 'xxxx' before Render' error. I understand why the problem occurs but I can't think of a solution. Help! Ideally what I'd like to do is simply call a method within the event that will update the UI, but I don't know if that's possible.

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• Checkbox alignment in Internet Explorer, Firefox and Chrome

  - by Andrej

  Checkbox alignment with its label (i.e., vertical centering) cross different web browsers makes me crazy. Pasted below is standard html code: <label for="ch"><input id="ch" type="checkbox">My Checkbox</label> I tested different CSS tricks (e.g., link 1, link 2); most solutions works fine in FF, but are completely off in Chrome or IE8. I'm looking for any references or pointers to solve this issue. Thanks in advance. EDIT According to Elq suggestion I modified the HTML <div class="row"> <input type="checkbox" id="ch1" /> <label for="ch1">Test</label> </div> and CSS .row{ display: table-row; } label{ display: table-cell; vertical-align: middle; } Works now in Firefox, Internet Explorer 8, and Chrome on Windows. Fails on Firefox and Chrome on Linux. Also works in Firefox and Safari on Mac, but fails on Chrome.

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• SQL trigger to delete rows from database

  - by wpearse

  I have an industrial system that logs alarms to a remotely hosted MySQL database. The industrial system inserts a new row whenever a property of the alarm changes (such as the time the alarm was activated, acknowledged or switched off) into a table named 'alarms'. I don't want multiple records for each alarm, so I have set up two database triggers. The first trigger mirrors each new record to a second table, creating/updating rows as required: CREATE TRIGGER `mirror_alarms` BEFORE INSERT ON `alarms` FOR EACH ROW INSERT INTO `alarm_display` (Tag,...,OffTime) VALUES (new.Tag,...,new.OffTime) ON DUPLICATE KEY UPDATE OnDate=new.OnDate,...,OffTime=new.OffTime The second trigger should execute after the first and (ideally) delete all rows from the alarms table. (I used the Tag property of the alarm because the Tag property never changes, although I suspect I could just use a 'DELETE FROM alarms WHERE 1' statement to the same effect). CREATE TRIGGER `remove_alarms` AFTER INSERT ON `alarms` FOR EACH ROW DELETE FROM alarms WHERE Tag=new.Tag My problem is that the second trigger doesn't appear to run, or if it does, the second trigger doesn't delete any rows from the database. So here's the question: why does my second trigger not do what I expect it to do?

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• Font advance calculation problem on Blackberry OS 5.0

  - by John

  I am currently working on my own implementation of a tab bar for a BlackBerry app, where each tab bar has a title that is right aligned (i.e. the last character in each should be the same distance from the right hand side of the screen). To work out where to draw the text I am using the following calculation: screen width - advance of title - indent. The font I am using is 'BBAlpha Sans' (height 28). Using BlackBerry OS 4.6 everything seems to be calculated properly and the text is aligned when I move between tabs, however I am finding that when I use OS 5.0 it doesn't calculate the advance properly and as a result the alignment is off by maybe 5 pixels or so. With the default font (also BBAlpha Sans, but height 24 - for OS 5.0 at least) it works fine in both versions.. but I don't necessarily always want to use the default font/size, so any ideas what could be going wrong? Is this a bug in the 5.0 API? Thanks. Code: public class TitleBarBackground extends Background { .. public void draw(Graphics graphics, XYRect rect) { graphics.pushRegion(rect); .. Font titleBarFont = FontFamily.forName("BBAlpha Sans").getFont(Font.PLAIN, 28); ... int textWidth = titleBarFont.getAdvance(title); graphics.drawText(title, rect.width - textWidth - TITLE_OFFSET, textYOffset); graphics.popContext(); } .. }

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• What is the easiest way to add compression to WCF in Silverlight?

  - by caryden

  I have a silverlight 2 beta 2 application that accesses a WCF web service. Because of this, it currently can only use basicHttp binding. The webservice will return fairly large amounts of XML data. This seems fairly wasteful from a bandwidth usage standpoint as the response, if zipped, would be smaller by a factor of 5 (I actually pasted the response into a txt file and zipped it.). The request does have the "Accept-Encoding: gzip, deflate" - Is there any way have the WCF service gzip (or otherwise compress) the response? I did find this link but it sure seems a bit complex for functionality that should be handled out-of-the-box IMHO. OK - at first I marked the solution using the System.IO.Compression as the answer as I could never "seem" to get the IIS7 dynamic compression to work. Well, as it turns out: Dynamic Compression on IIS7 was working al along. It is just that Nikhil's Web Developer Helper plugin for IE did not show it working. My guess is that since SL hands the web service call off to the browser, that the browser handles it "under the covers" and Nikhil's tool never sees the compressed response. I was able to confirm this by using Fiddler which monitors traffic external to the browser application. In fiddler, the response was, in fact, gzip compressed!! The other problem with the System.IO.Compression solution is that System.IO.Compression does not exist in the Silverlight CLR. So from my perspective, the EASIEST way to enable WCF compression in Silverlight is to enable Dynamic Compression in IIS7 and write no code at all.

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• How to set App as site.com/ in Kohana3

  - by Drew

  Hi all! I've only just started using Kohana ( 3 hours ago), and so far it's blown my socks off (and I'm wearing slippers, so that's quite impressive). Right now, I have a controller 'Controller_FrontPage' with associated views and models and I'm trying to get it accesible from the root of my website (eg, http://www.mysite.com/). If I edit the default controller in the bootstrap from: Route::set('default', '(<controller>(/<action>(/<id>)))') ->defaults(array( 'controller' => 'welcome', 'action' => 'index', )); to 'controller' => '', I get an error, could not find controller_ (which makes sense), and if I change it to 'controller' => '/', I get an error, could not find controller_/ (which also makes sense). If I set 'controller' => 'FrontPage', everything works fine, but all my links (html::anchor(...)) point to http://www.mysite.com/FrontPage/*. Is there a way to have all the anchors point to http://www.mysite.com/*?

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• Help me write my LISP :) LISP environments, Ruby Hashes...

  - by MikeC8

  I'm implementing a rudimentary version of LISP in Ruby just in order to familiarize myself with some concepts. I'm basing my implementation off of Peter Norvig's Lispy (http://norvig.com/lispy.html). There's something I'm missing here though, and I'd appreciate some help... He subclasses Python's dict as follows: class Env(dict): "An environment: a dict of {'var':val} pairs, with an outer Env." def __init__(self, parms=(), args=(), outer=None): self.update(zip(parms,args)) self.outer = outer def find(self, var): "Find the innermost Env where var appears." return self if var in self else self.outer.find(var) He then goes on to explain why he does this rather than just using a dict. However, for some reason, his explanation keeps passing in through my eyes and out through the back of my head. Why not use a dict, and then inside the eval function, when a new "sub-environment" needs to be created, just take the existing dict and update the key/value pairs that need to be updated, and pass that new dict into the next eval? Won't the Python interpreter keep track of the previous "outer" envs? And won't the nature of the recursion ensure that the values are pulled out from "inner" to "outer"? I'm using Ruby, and I tried to implement things this way. Something's not working though, and it might be because of this, or perhaps not. Here's my eval function, env being a regular Hash: def eval(x, env = $global_env) ........ elsif x[0] == "lambda" then ->(*args) { eval(x[2], env.merge(Hash[*x[1].zip(args).flatten(1)])) } ........ end The line that matters of course is the "lambda" one. If there is a difference, what's importantly different between what I'm doing here and what Norvig did with his Env class? If there's no difference, then perhaps someone can enlighten me as to why Norvig uses the Env class. Thanks :)

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• Learning libraries without books or tutorials

  - by Kawili-wili

  While many ask questions about where to find good books or tutorials, I'd like to take the opposite tack. I consider myself to be an entry-level programmer ready to move up to mid-level. I have written code in c, c++, c#, perl, python, clojure, vb, and java, so I'm not completely clueless. Where I see a problem in moving to the next level is learning to make better use of the literally hundreds upon hundreds of libraries available out there. I seem paralyzed unless there is a specific example in a book or tutorial to hand-hold me, yet I often read in various forums where another programmer attempts to assist with a question. He/she will look through the docs or scan the available classes/methods in their favorite IDE and seem to grok what's going on in a relatively short period of time, even if they had no previous experience with that specific library or function. I yearn to break the umbilical chord of constantly spending hour upon hour searching and reading, searching and reading, searching and reading. Many times there is no book or tutorial, or if there is, the discussion glosses over my specific needs or the examples shown are too far off the path for the usage I had in mind or the information is outdated and makes use of deprecated components or the library itself has fallen out of mainstream, yet is still perfectly usable (but no docs, books, or tutorials to hand-hold). My question is: In the absence of books or tutorials, what is the best way to grok new or unfamiliar libraries? I yearn to slicken the grok path so I can get down to the business of doing what I love most -- coding.

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• Methods to Analyze Sell Orders (in a video game)

  - by Travis

  I'm building a market manager for EVE, but this problem should be solvable without any prior knowledge of the game. Basically, sell orders in EVE look like this: All I'm really concerned with is picking a good price. The numbers the program would pick are sent out to our production team so they can buy the items to build things. Just like in a real market, the numbers we send off need to reflect the cheapest price that still offers a good quantity. Also, available quantities change over time, so we can't just pick the lowest listed price. For example, in the screencap above, we would set the sell price between 2,800.00 ISK and 3,000.00 ISK, even if only 500 units were needed. Even though the cheapest order would fit the quantity, it would probably quickly disappear. It would be better to set the price a tad higher so we don't underpay the production people. The Question: It's easy enough to figure prices out just by looking at the data, but I can't figure out how to have a program [java] do it. Different items sell with much less or more quantities (i.e. 3 or 300 or 3000 items) so the program has to be able to modify itself based on the offerings. I don't really want code as much as I do a way to think this through. Thanks in advance.

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• How to check for mip-map availability in OpenGL?

  - by Xavier Ho

  Recently I bumped into a problem where my OpenGL program would not render textures correctly on a 2-year-old Lenovo laptop with an nVidia Quadro 140 card. It runs OpenGL 2.1.2, and GLSL 1.20, but when I turned on mip-mapping, the whole screen is black, with no warnings or errors. This is my texture filter code: glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE); After 40 minutes of fiddling around, I found out mip-mapping was the problem. Turning it off fixed it: // glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); // glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE); I get a lot of aliasing, but at least the program is visible and runs fine. Finally, two questions: What's the best or standard way to check if mip-mapping is available on a machine, aside from checking OpenGL versions? If mip-mapping is not available, what's the best work-around to avoid aliasing?

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• Ember Data Sycn - LocalStorage+REST+RealTime+Online/Offline

  - by Miguel Madero

  We have a combination of requirements in terms o data access. Pre-load some reference data. We need reference data to survive browser restarts instead of just living in memory to avoid loading it all the time. I'm currently using the LocalStorageAdapter for that. Once we have it, we would like to sync changes (polling or using Socket.IO in the background and updating the LocalStorage could do the trick) There're other models that are more transactional, where we would need to directly go to the Server and get/save them. It would be nice to use something like the RESTAdapter for that. Lastly, there're some operations that should work off-line and changes should be synced later. To make it more concrete: * We pre-load vendor and "favorite products" into Local Storage. We work offline with those. * We need to sync server changes to vendor and product information. * If they search the full catalog, that requires them to be online. * When offline, we need to allow users to add something to their cart or even submit and order. We would like to queue this action and submit it when they have an Internet Connection. So a few questions are derived from this: * Is there a way to user RESTAdapter in combination with LocalStorage? * Is there some Socket.IO support? (Happy to do this part manually) * Is there Queueing support? Ideally at the Ember-Data level. I know we will have to do a lot of this manually and pull together the different lego pieces, but I wanted to ask for some perspective from experience Ember devs.

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