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  • Avoiding explicit recursion in Haskell

    - by Travis Brown
    The following simple function applies a given monadic function iteratively until it hits a Nothing, at which point it returns the last non-Nothing value. It does what I need, and I understand how it works. lastJustM :: (Monad m) => (a -> m (Maybe a)) -> a -> m a lastJustM g x = g x >>= maybe (return x) (lastJustM g) As part of my self-education in Haskell I'm trying to avoid explicit recursion (or at least understand how to) whenever I can. It seems like there should be a simple non-explicitly recursive solution in this case, but I'm having trouble figuring it out. I don't want something like a monadic version of takeWhile, since it could be expensive to collect all the pre-Nothing values, and I don't care about them anyway. I checked Hoogle for the signature and nothing shows up. The m (Maybe a) bit makes me think a monad transformer might be useful here, but I don't really have the intuitions I'd need to come up with the details (yet). It's probably either embarrassingly easy to do this or embarrassingly easy to see why it can't or shouldn't be done, but this wouldn't be the first time I've used self-embarrassment as a pedagogical strategy. Background: Here's a simplified working example for context: suppose we're interested in random walks in the unit square, but we only care about points of exit. We have the following step function: randomStep :: (Floating a, Ord a, Random a) => a -> (a, a) -> State StdGen (Maybe (a, a)) randomStep s (x, y) = do (a, gen') <- randomR (0, 2 * pi) <$> get put gen' let (x', y') = (x + s * cos a, y + s * sin a) if x' < 0 || x' > 1 || y' < 0 || y' > 1 then return Nothing else return $ Just (x', y') Something like evalState (lastJustM (randomStep 0.01) (0.5, 0.5)) <$> newStdGen will give us a new data point.

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  • Retrieving data from a JSON sub array in javascript, where identifier starts with an integer

    - by Archie Ec
    I must be missing something simple here, but I'm having trouble retrieving data from a JSON array response. I can access objects with identifiers that start with letters, but not ones that start with numbers. For example, I can access data.item[0].specs.overview.details But I can't access data.item[0].specs.9a99.details If anyone can point me in the right direction, I'd really appreciate it. Thanks.

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  • Flex bug?? Get messed up stacked ColumnChart with type="100%"

    - by Nir
    I am trying to do a stacked Column chart with type="100%" and a mixture of positive and negative values. When all the values are positive, is functions well, but when negative numbers come to the game, it looks totally messed up. When I also look at Adobe documentation (look here), I see the following code for stacked column chart involving negative numbers: <?xml version="1.0"?> <!-- charts/StackedNegative.mxml --> <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"> <mx:Script><![CDATA[ import mx.collections.ArrayCollection; [Bindable] public var expenses:ArrayCollection = new ArrayCollection([ {Month:"Jan", Profit:-2000, Expenses:-1500}, {Month:"Feb", Profit:1000, Expenses:-200}, {Month:"Mar", Profit:1500, Expenses:-500} ]); ]]></mx:Script> <mx:Panel title="Column Chart"> <mx:ColumnChart id="myChart" dataProvider="{expenses}" showDataTips="true"> <mx:horizontalAxis> <mx:CategoryAxis dataProvider="{expenses}" categoryField="Month" /> </mx:horizontalAxis> <mx:series> <mx:ColumnSet type="stacked" allowNegativeForStacked="true"> <mx:series> <mx:ColumnSeries xField="Month" yField="Profit" displayName="Profit" /> <mx:ColumnSeries xField="Month" yField="Expenses" displayName="Expenses" /> </mx:series> </mx:ColumnSet> </mx:series> </mx:ColumnChart> <mx:Legend dataProvider="{myChart}"/> </mx:Panel> </mx:Application> It works fine. But try to change: <mx:ColumnSet type="stacked" allowNegativeForStacked="true"> to: <mx:ColumnSet type="100%" allowNegativeForStacked="true"> and you'll see that it doesn't on January data, where both values are negative, the chart shows as if they are positive, and on the other two where one value is positive and the other is negative, it shows only the positive part as 100%... Isn't it a Flex Bug? I have my own case with such data and it behaves wrong the same way. I'd expect that if it has 800 stacked on -200, it will show 80% up and 20% down, totalling 100%. BTW: Using Flex 4, though these are all mx components. Thanks a lot and regards from Berlin, Germany, Nir.

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  • Mysql / Django - Begin auto increment to 1

    - by ark
    Hi, I have a django script which loads data, the beginning of the script deletes all datas in database. So when I execute 1st time this script, the auto increment primary keys begin to 1 to 15 (if 15 objects) and if I want to reload data, I reexecute the script. My issue is when I execute it again, pks numbers begin to 16 (for 2nd launch), I would like each time auto_increment begins to 1, is it possible whitout regenerating tables structure each time ? Thanks

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  • parse my proprietary string format

    - by microsumol
    How can we get the numbers 7 and 4 and 5 from the following string: MODULE potmtpMAIN main <info: "Enterprise Optimizer 7.4 for COR Technology 5.5 -- Advanced Solver Edition", url:"http://EO.riverlogic.com", url_menu:"EO Online...", app_id:"EOAS",app_name:"Enterprise Optimizer AS", app_major:7, app_minor:4,app_micro:5,app_copyright:"\251 1996-2010 River Logic Inc.\r\nAll Rights Reserved."> The search must be based on app_major: app_minor: and app_micro Thank You in advance

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  • How to fill a two Dimensional ArrayList in java with Integers?

    - by eNetik
    I have to create a 2d array with unknown size. So I have decided to go with a 2d ArrayList the problem is I'm not sure how to initialize such an array or store information. Say I have the following data 0 connects 1 2 connects 3 4 connects 5 ....etc up to a vast amount of random connections and I want to insert true(1) into [0][1], true(1) into [2][3], true(1) into [4][5]. Can the array automatically update the column/rows for me Any help is appreciated thanks

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  • Is there a better way to write this .htaccess directive?

    - by Bill H
    I want all css, javascript, and image file requests, that are named like this "filename.12345.css" to be re-routed to "filename.css". The ".12345" part will always be numbers and the length can be anywhere from 11 - 15 characters. This directive seems to work OK but I want to make sure there is no error in my logic. RewriteRule ^(.+)\.(.+)\.(js|css|jpg|gif|png)$ $1.$3 Any help would be greatly

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  • Breaking a simple Captcha

    - by maSnun
    Hello All, For testing purpose, I need to break this captcha: http://wapforum.us/web/img.php As you can see, this is a very simple captcha with only 4 digits of numbers. Any sample code will be highly appreciated. Thanks and Regards, Masnun

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  • Display a variable when a select box option is selected

    - by user782104
    For example, the select box <select><option selected="" value="">Please Select</option><option value='txt'>Text</option><option value='int'>Numbers</option><option value='bool' >Boolean</option></select> has a string $messageList=array ( 'txt'=>'text message', 'int'=>'int message','bool'=>'bool message'); What i would like to achieve is to display correspond message when the optition is select?

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  • String tokens in .NET

    - by julio
    I am writing a app in .NET which will generate random text based on some input. So if I have text like "I love your {lovely|nice|great} dress" I want to choose randomly from lovely/nice/great and use that in text. Any suggestions in C# or VB.NET are welcome.

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  • How can I ignore .svn directories when using sloccount?

    - by digitala
    I'm trying to use sloccount from within hudson to gather statistics on our codebase, however by default sloccount collects information on all files, even those which are "hidden" (eg. .hideme). This means the statistics are skewed since they include numbers from files within the .svn directories. Is there any way I can tell sloccount to correctly ignore any files/directories which start with a .?

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  • C# Extension Method for String Data Type

    - by Jimbo
    My web application deals with strings that need to be converted to numbers alot - users often put commas, currency symbols etc. in these fields so what I want to do is create a string extension method that cleans the field up and converts it to a decimal. For example: decimal myNumber = "$1,250.85".ToDecimal(); Can anyone help with this? Thanks!

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  • c program tringle

    - by Johnathon
    C program that accepts three integer values from the user representing the three sides of a triangle. echo whether the 3 numbers makes a equilateral, scalene or isosceles triangle.

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  • Application Profiling: Memory Usage

    - by Abs
    Hello all, I have switched on the Codeigniter profile (very useful) and I have noticed that a page of mine shows the memory used as: 2,405,496 bytes That's ~2MB and it's for one request - does it mean if 1000 users accessed this page at the same time, memory usage will be 2GB? Have I got my maths wrong or is there more to this than just multiplying two numbers? Thanks all for any help

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  • C++ program to calculate large factorials

    - by xbonez
    How can I write a c++ program to calculate large factorials. Example, if I want to calculate (100!) / (99!), we know the answer is 100, but if i calculate the factorials of the numerator and denominator individually, both the numbers are gigantically large.

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  • Change Number Format

    - by gsembilan
    I have a lot lines contains XXXXXXXXX number format. I want change number XXXXXXXXX to XX.XXX.XXX.X XXXXXXXXX = 9 digit random number Anyone can help me? Thanks in advance

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  • a console code editor with CUA (ctrl-x ctrl-v ...) key bindings (unlike vi)

    - by clyfe
    I'm searching for a console code editor with CUA key bindings (ctrl-x c v etc.) Right now i'm toying mcedit but i don't really like it. My desired features are: * be fast * CUA key bindings (ctrl-x c v etc.) * toggle show line numbers * find/replace/goto line * bind custom keys to action( ctrl-shift-arrowdown to double the curent line etc.) * nice simple vi-like interface (no pointless menus) * be able to programatically extend it ... etc.

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  • How to grab data on website?

    - by Doug
    So, often, I check my accounts for different numbers. For example, my affiliate accounts- i check for cash increase. I want to program a script where it can login to all these websiets and then grab the money value for me and display it on one page. How can I program this?

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