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  • Creating an Interface To a Language's Standard Library?

    - by Nathan Arthur
    In the process of learning test-driven development, I've been introduced to dependency injection and the use of interfaces, and have started using these concepts in my own PHP code in order to make it more testable. There have been times when I've needed to test code that was doing things like calling the PHP time() function. In order to make these tests predictable, it seemed logical to create an interface to the standard PHP functions I use so that I can mock them out in my tests. Is this good software design? What are the pros and cons of doing this? I've found myself groaning at how quickly my PHP interface can stick its fingers into everything I do. Is there a better way to make code that relies on PHP-accessed state and functions more testable?

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  • Overview of XSLT

    - by kaleidoscope
    XSLT (Extensible Stylesheet Language Transformations) is a declarative- XMLbased language used for the transformation of XML documents into other XML documents. Using XSLT , the original document does not changed; rather, a new document is created based on the content of an existing one. XSLT is developed by the World Wide Web Consortium (W3C).   Using XSLT we can transform source xml file into another xml file, word file or Excel file.    XSLT Functions : -   There are the following built - in XSLT functions :   Name Description current() Returns the current node document() Used to access the nodes in an external XML document element-available() Tests whether the element specified is supported by the XSLT processor format-number() Converts a number into a string function-available() Tests whether the function specified is supported by the XSLT processor generate-id() Returns a string value that uniquely identifies a specified node key() Returns a node-set using the index specified by an <xsl:key> element system-property() Returns the value of the system properties unparsed-entity-uri() Returns the URI of an unparsed entity   For more information –   http://www.w3schools.com/xsl/default.asp   Technorati Tags: Ritesh, Overview of XSLT

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  • Lazy Processing of Streams

    - by Giorgio
    I have the following problem scenario: I have a text file and I have to read it and split it into lines. Some lines might need to be dropped (according to criteria that are not fixed). The lines that are not dropped must be parsed into some predefined records. Records that are not valid must be dropped. Duplicate records may exist and, in such a case, they are consecutive. If duplicate / multiple records exist, only one item should be kept. The remaining records should be grouped according to the value contained in one field; all records belonging to the same group appear one after another (e.g. AAAABBBBCCDEEEFF and so on). The records of each group should be numbered (1, 2, 3, 4, ...). For each group the numbering starts from 1. The records must then be saved somewhere / consumed in the same order as they were produced. I have to implement this in Java or C++. My first idea was to define functions / methods like: One method to get all the lines from the file. One method to filter out the unwanted lines. One method to parse the filtered lines into valid records. One method to remove duplicate records. One method to group records and number them. The problem is that the data I am going to read can be too big and might not fit into main memory: so I cannot just construct all these lists and apply my functions one after the other. On the other hand, I think I do not need to fit all the data in main memory at once because once a record has been consumed all its underlying data (basically the lines of text between the previous record and the current record, and the record itself) can be disposed of. With the little knowledge I have of Haskell I have immediately thought about some kind of lazy evaluation, in which instead of applying functions to lists that have been completely computed, I have different streams of data that are built on top of each other and, at each moment, only the needed portion of each stream is materialized in main memory. But I have to implement this in Java or C++. So my question is which design pattern or other technique can allow me to implement this lazy processing of streams in one of these languages.

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  • Who could ask for more with LESS CSS? (Part 1 of 3&ndash;Features)

    - by ToStringTheory
    It wasn’t very long ago that I first began to get into CSS precompilers such as SASS (Syntactically Awesome Stylesheets) and LESS (The Dynamic Stylesheet Language) and I had been hooked on the idea since.  When I finally had a new project come up, I leapt at the opportunity to try out one of these languages. Introduction To be honest, I was hesitant at first to add either framework as I didn’t really know much more than what I had read on their homepages, and I didn’t like the idea of adding too much complexity to a project - I couldn’t guarantee I would be the only person to support it in the future. Thankfully, both of these languages just add things into CSS.  You don’t HAVE to know LESS or SASS to do anything, you can still do your old school CSS, and your output will be the same.  However, when you want to start doing more advanced things such as variables, mixins, and color functions, the functionality is all there for you to utilize. From what I had read, SASS has a few more features than LESS, which is why I initially tried to figure out how to incorporate it into a MVC 4 project. However, through my research, I couldn’t find a way to accomplish this without including some bit of the Ruby on Rails framework on the computer running it, and I hated the fact that I had to do that.  Besides SASS, there is little chance of me getting into the RoR framework, at least in the next couple years.  So in the end, I settled with using LESS. Features So, what can LESS (or SASS) do for you?  There are several reasons I have come to love it in the past few weeks. 1 – Constants Using LESS, you can finally declare a constant and use its value across an entire CSS file. The case that most people would be familiar with is colors.  Wanting to declare one or two color variables that comprise the theme of the site, and not have to retype out their specific hex code each time, but rather a variable name.  What’s great about this is that if you end up having to change it, you only have to change it in one place.  An important thing to note is that you aren’t limited to creating constants just for colors, but for strings and measurements as well. 2 – Inheritance This is a cool feature in my mind for simplicity and organization.  Both LESS and SASS allow you to place selectors within other selectors, and when it is compiled, the languages will break the rules out as necessary and keep the inheritance chain you created in the selectors. Example LESS Code: #header {   h1 {     font-size: 26px;     font-weight: bold;   }   p {     font-size: 12px;     a     {       text-decoration: none;       &:hover {         border-width: 1px       }     }   } } Example Compiled CSS: #header h1 {   font-size: 26px;   font-weight: bold; } #header p {   font-size: 12px; } #header p a {   text-decoration: none; } #header p a:hover {   border-width: 1px; } 3 - Mixins Mixins are where languages like this really shine.  The ability to mixin other definitions setup a parametric mixin.  There is really a lot of content in this area, so I would suggest looking at http://lesscss.org for more information.  One of the things I would suggest if you do begin to use LESS is to also grab the mixins.less file from the Twitter Bootstrap project.  This file already has a bunch of predefined mixins for things like border-radius with all of the browser specific prefixes.  This alone is of great use! 4 – Color Functions This is the last thing I wanted to point out as my final post in this series will be utilizing these functions in a more drawn out manner.  Both LESS and SASS provide functions for getting information from a color (R,G,B,H,S,L).  Using these, it is easy to define a primary color, and then darken or lighten it a little for your needs.  Example: Example LESS Code: @base-color: #111; @red:        #842210; #footer {   color: (@base-color + #003300);   border-left:  2px;   border-right: 2px;   border-color: desaturate(@red, 10%); } Example Compiled CSS: #footer {    color: #114411;    border-left:  2px;    border-right: 2px;    border-color: #7d2717; } I have found that these can be very useful and powerful when constructing a site theme. Conclusion I came across LESS and SASS when looking for the best way to implement some type of CSS variables for colors, because I hated having to do a Find and Replace in all of the files using the colors, and in some instances, you couldn’t just find/replace because of the color choices interfering with other colors (color to replace of #000, yet come colors existed like #0002bc).  So in many cases I would end up having to do a Find and manually check each one. In my next post, I am going to cover how I’ve come to set up these items and the structure for the items in the project, as well as the conventions that I have come to start using.  In the final post in the series, I will cover a neat little side project I built in LESS dealing with colors!

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  • Is a function plotter a legitimate use of eval() in JavaScript?

    - by moose
    From PHP development I know that eval is evil and I've recently read What constitutes “Proper use” of the javascript Eval feature? and Don't be eval. The only proper use of eval I've read is Ajax. I'm currently developing a visualization tool that lets users see how polynomials can interpolate functions: Example Code on GitHub I use eval for evaluation of arbitrary functions. Is this a legitimate use of eval? How could I get rid of eval? I want the user to be able to execute any function of the following forms: a x^i with a,i in R sin, cos, tan b^x with b in R any combination that you can get by adding (e.g. x^2 + x^3 + sin(x)), multiplying (e.g. sin(x)*x^2) or inserting (e.g. sin(x^2))

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  • Which game library/engine to choose?

    - by AllTheThingsSheSaid
    I'm not a programming beginner at all. I've tried 2 libraries/engines so far, allegro and Unity. For allegro. i think its not good if i wanna make a career in gaming industry since its not powerful enough. I don't feel comfortable with unity. Its more like a software like photoshop or flash. You can do almost everything with pre-defined functions, tools and with less coding. I need something which offers less tools and pre defined functions and more coding work. It would be awesome if its free and c/c++ based. I need both 2D/3D. and please, don't tell me to make my own library, i am not "that" advance. Any other information about gaming industry would be greatly appreciated.

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  • How can I improve these online java programming puzzles I wrote for my (middle/high school) students?

    - by Arcymag
    I'm teaching some middle and high school students programming right now, and I found that some of them really liked online programming puzzles. So I created http://www.kapparate.com/coder/ , and right now there's 4 categories of puzzles. All the puzzles are set up right now so that variables are pre-initialized, and the user plugs in some code in the middle. For example, the problem might say these are pre-initialized: int x = ????; int y = ????; int z; and then the program might ask the student to write the final line of code: z = x + y;. Now I know I could go a long way in improving the usability of this site (like having an area that lists the pre-defined variables), but I was wondering if this concept seems sound. I know some sites have kids fill in functions, but not all of my students know what functions are yet, and I'm trying to introduce online programming puzzles before that.

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  • In what way I can implement packet filtering function in C++/C#?

    - by Network study
    Background: I am going to design a firewall-like application (with GUI) which will include several functions such as Packet sniffing and packet filtering. Both of the functions should be implemented to support different protocol levels including application, transport, network and link layer. I only know a little in C#.Net programming to perform the IP packet sniffing. It is also known that packet filtering requires the techniques in WFP or LSP and packet sniffing in application requires dll hooking. Questions: I am not sure which programming language(either C++ or C#) would be suitable for designing such an application described above. If I want to implement the packet filtering function, any libraries will be needed? edit01: Someone suggest that winDivert would be helpful, is it true?

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  • What programming language matches this description? [on hold]

    - by Benubird
    I am looking for a functional language that is basically dynamic programming - i.e. one where functions are first-class objects - but where all function calls are asynchronous by default; i.e. you define function X(a,b) = (Y(a)+Z(b)), and when X() is called, it sees it is waiting for the return from two functions, runs one in the current thread, and spawns a new thread to run the other. The future is very much parallel processing; multiple cores, multiple machines, the internet of things, etc. and I was wondering if there was a language specifically designed to make this kind of parallelization easy. I currently have only used imperative languages (c, php, java, ruby, etc), so I don't know anything about what kind of functional languages are available.

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  • Separate parts of a game engine [on hold]

    - by user272716
    I'm pretty new in developing videogames. By now I only used SDL with C/C++ to create games. I'm currently learning OpenGL and I realized that to be fluid and easy to maintain the code must be logically separated. Since I want to use OpenGLES on iOS and Android I was wondering how the engine must be imagined in a technical way, some questions came up: Do I have to separate input/update functions from draw functions in different threads? Is there only one proper way to think a game engine/loop? What kind of assets should I use to create a 3D game using openGl ES to get better performance?

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  • Application window as polygon texture?

    - by nekome
    Is there a way, or method, to have some application rendered as texture in 3D scene on some polygon, and also have full interactivity with it? I'm talking about Windows platform, and maybe OpenGL but I guess it doesn't matter is it OGL or DX. For example: I run Calculator using WINAPI functions (preferably hidden, not showing on desktop) and I want to render it inside 3D scene on some polygon but still be able to type or click buttons and have it respond. My idea to realize this is to have WINAPI take screenshot (or render it to memory if possible) of that Calculator and pass it to OpenGL as texture for each frame (I'm experimenting with SDL through pygame) and for mouse interactivity to use coordination translation and calculate where on application window it would act, and then use WINAPI functions such as SetCursorPos to set cursor ant others to simulate click or something else. I haven't found any tutorials with topic similar to this one. Am I on a right track? Is there better way to do this if possible at all?

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  • How do I correctly multiply an XMMATRIX by a scalar?

    - by user43129
    Using DirectXMath and its XMMATRIX structure in C++ and Direct X 11, how does one multiply that matrix structure by a single float scalar? I want to implement the operation B = A * f; where A and B are XMMATRIX and f is a float. I found all sorts of functions to multiply a matrix by another matrix or a vector. I found all sorts of functions to construct matrices. I could find no scalar multiplication! Why is there no such function? Is there no use case? Did I miss something? How do I implement scalar multiplication?

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  • Assertion failure when trying to write (INSERT, UPDATE) to sqlite database on iPhone.

    - by Mark McFarlane
    I have a really frustrating error that I've spent hours looking at and cannot fix. I can get data from my db no problem with this code, but inserting or updating gives me these errors: *** Assertion failure in +[Functions db_insert_answer:question_type:score:], /Volumes/Xcode/Kanji/Classes/Functions.m:129 *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Error inserting: db_insert_answer:question_type:score:' Here is the code I'm using: [Functions db_insert_answer:[[dict_question objectForKey:@"JISDec"] intValue] question_type:@"kanji_meaning" score:arc4random() % 100]; //update EF, Next_question, n here [Functions db_update_EF:[dict_question objectForKey:@"question"] EF:EF]; To call these functions: +(sqlite3_stmt *)db_query:(NSString *)queryText{ sqlite3 *database = [self get_db]; sqlite3_stmt *statement; NSLog(queryText); if (sqlite3_prepare_v2(database, [queryText UTF8String], -1, &statement, nil) == SQLITE_OK) { } else { NSLog(@"HMM, COULDNT RUN QUERY: %s\n", sqlite3_errmsg(database)); } sqlite3_close(database); return statement; } +(void)db_insert_answer:(int)obj_id question_type:(NSString *)question_type score:(int)score{ sqlite3 *database = [self get_db]; sqlite3_stmt *statement; char *errorMsg; char *update = "INSERT INTO Answers (obj_id, question_type, score, date) VALUES (?, ?, ?, DATE())"; if (sqlite3_prepare_v2(database, update, -1, &statement, nil) == SQLITE_OK) { sqlite3_bind_int(statement, 1, obj_id); sqlite3_bind_text(statement, 2, [question_type UTF8String], -1, NULL); sqlite3_bind_int(statement, 3, score); } if (sqlite3_step(statement) != SQLITE_DONE){ NSAssert1(0, @"Error inserting: %s", errorMsg); } sqlite3_finalize(statement); sqlite3_close(database); NSLog(@"Answer saved"); } +(void)db_update_EF:(NSString *)kanji EF:(int)EF{ sqlite3 *database = [self get_db]; sqlite3_stmt *statement; //NSLog(queryText); char *errorMsg; char *update = "UPDATE Kanji SET EF = ? WHERE Kanji = '?'"; if (sqlite3_prepare_v2(database, update, -1, &statement, nil) == SQLITE_OK) { sqlite3_bind_int(statement, 1, EF); sqlite3_bind_text(statement, 2, [kanji UTF8String], -1, NULL); } else { NSLog(@"HMM, COULDNT RUN QUERY: %s\n", sqlite3_errmsg(database)); } if (sqlite3_step(statement) != SQLITE_DONE){ NSAssert1(0, @"Error updating: %s", errorMsg); } sqlite3_finalize(statement); sqlite3_close(database); NSLog(@"Update saved"); } +(sqlite3 *)get_db{ sqlite3 *database; NSFileManager *fileManager = [NSFileManager defaultManager]; NSString *copyFrom = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"/kanji_training.sqlite"]; if([fileManager fileExistsAtPath:[self dataFilePath]]) { //NSLog(@"DB FILE ALREADY EXISTS"); } else { [fileManager copyItemAtPath:copyFrom toPath:[self dataFilePath] error:nil]; NSLog(@"COPIED DB TO DOCUMENTS BECAUSE IT DIDNT EXIST: NEW INSTALL"); } if (sqlite3_open([[self dataFilePath] UTF8String], &database) != SQLITE_OK) { sqlite3_close(database); NSAssert(0, @"Failed to open database"); NSLog(@"FAILED TO OPEN DB"); } else { if([fileManager fileExistsAtPath:[self dataFilePath]]) { //NSLog(@"DB PATH:"); //NSLog([self dataFilePath]); } } return database; } + (NSString *)dataFilePath { NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [paths objectAtIndex:0]; return [documentsDirectory stringByAppendingPathComponent:@"kanji_training.sqlite"]; } I really can't work it out! Can anyone help me? Many thanks.

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  • certain Smarty tags don't work in OpenX templates

    - by mikez302
    I am on a team that is developing an OpenX plugin, and I am responsible for the UI. I noticed that if I use certain Smarty tags in my template, the app doesn't work and I see an error message, similar to this: Plugin by name 'Html_select_date' was not found in the registry; used paths: default_views_helpers_: /openx/www/admin/plugins/myApp/application/modules/default/views/helpers/ OX_OXP_UI_View_Helper_: /openx/www/admin/plugins/myApp/application/../library/OX/OXP/UI/View/Helper/ OX_UI_View_Helper_: /openx/www/admin/plugins/myApp/application/../library/OX/UI/View/Helper/ Zend_View_Helper_: Zend/View/Helper/ (stack trace) The stack trace looks like this: #0 /openx/www/admin/plugins/myApp/library/Zend/View/Abstract.php(1117): Zend_Loader_PluginLoader-load('Html_select_dat...') #1 /openx/www/admin/plugins/myApp/library/Zend/View/Abstract.php(568): Zend_View_Abstract-_getPlugin('helper', 'html_select_dat...') #2 /openx/www/admin/plugins/myApp/library/OX/UI/Smarty/SmartyWithViewHelper.php(25): Zend_View_Abstract-getHelper('html_select_dat...') #3 /openx/var/templates_compiled/%2Fdefault%2Fviews%2Fscripts%2Findex%2Fview-reports.html^%%E8^E80^E80B56F2%%view-reports.html.php(38): OX_UI_Smarty_SmartyWithViewHelper-callViewHelper('html_select_dat...', Array) #4 /openx/lib/smarty/Smarty.class.php(1274): include('/openx...') #5 /openx/www/admin/plugins/myApp/library/OX/UI/View/SmartyView.php(103): Smarty-fetch('/openx...') #6 /openx/www/admin/plugins/myApp/library/Zend/View/Abstract.php(832): OX_UI_View_SmartyView-_run('/openx...') #7 /openx/www/admin/plugins/myApp/library/OX/UI/View/SmartyView.php(151): Zend_View_Abstract-render('index/view-repo...') #8 /openx/www/admin/plugins/myApp/library/OX/UI/View/Helper/WithViewScript.php(23): OX_UI_View_SmartyView-render('index/view-repo...') #9 /openx/www/admin/plugins/myApp/application/modules/default/views/helpers/ViewReports.php(5): OX_UI_View_Helper_WithViewScript::renderViewScript('index/view-repo...', Array) #10 /openx/www/admin/plugins/myApp/application/modules/default/controllers/IndexController.php(98): Default_Views_Helpers_ViewReports-renderPage() #11 /openx/www/admin/plugins/myApp/library/Zend/Controller/Action.php(512): IndexController-viewReportsAction() #12 /openx/www/admin/plugins/myApp/library/Zend/Controller/Dispatcher/Standard.php(288): Zend_Controller_Action-dispatch('viewReportsActi...') #13 /openx/www/admin/plugins/myApp/library/Zend/Controller/Front.php(945): Zend_Controller_Dispatcher_Standard-dispatch(Object(Zend_Controller_Request_Http), Object(Zend_Controller_Response_Http)) #14 /openx/www/admin/plugins/myApp/application/bootstrap.php(117): Zend_Controller_Front-dispatch() #15 /openx/www/admin/plugins/myApp/public/index.php(7): require('/openx...') #16 {main} This does not happen with all Smarty tags. For example, I can use {if}, {foreach}, or {assign} tags without any problems. But whenever I try to use {html_select_date}, {html_image}, or {html_table}, I get the errors. In case this matters, the programmer who is designing the plugin copied the openXWorkflow plugin and made some changes. I noticed that the openXWorkflow plugin has a file (openx/plugins_repo/openXWorkflow/www/admin/plugins/openXWorkflow/library/OX/UI/Smarty/SmartyCompilerWithViewHelper.php) with a class that overrides the default Smarty compiler, supposedly with the ability to compile shorthands for calling ZF view helpers. That file has a list of Smarty functions, but the list is incomplete. If I add the functions to the list, or simply delete the file, my template works fine, but I don't like to change library files. It may make the app hard to maintain, and I don't know if it will mess up something else. The file has the comment "There is no easy access to the list of Smarty's built-in functions so we need to list them here. HTML-specific functions are not included as we cover HTML generation separately.", so it seems like certain Smarty functions may be disabled on purpose for some reason. Will anything bad happen if I try to use them? If, for example, I want to use the {html_select_date} tag in my template, how would I go about doing that? Keep in mind that much of this stuff is new and unfamiliar to me. This is my first time ever using OpenX or Smarty, and I only have a little bit of experience with the Zend framework. Please let me know if we are using the wrong approach.

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  • JavaScript String Library - Hitting a Minor Roadblock

    - by OneNerd
    Ok - am trying to create a string library that contains a handful of useful things missing from JavaScript. Here is what I have so far: ;function $__STRING__$(in_string) { /* internal functions */ this.s = in_string; this.toString = function(){return this.s;}; /******* these functions CAN be chained (they return the $__STRING__$ object) ******/ this.uppercase = function(){this.s = this.s.toUpperCase(); return this;}; this.lowercase = function(){this.s = this.s.toLowerCase(); return this;}; this.trim = function(){this.s = this.s.replace(/^\s+|\s+$/g,""); return this;}; this.ltrim = function(){this.s = this.s.replace(/^\s+/,""); return this;}; this.rtrim = function(){this.s = this.s.replace(/\s+$/,""); return this;}; this.striptags = function(){this.s = this.s.replace(/<\/?[^>]+(>|$)/g, ""); return this;}; this.escapetags = function(){this.s = this.s.replace(/</g,"<").replace(/>/g,">"); return this;}; this.unescapetags = function(){this.s = this.s.replace(/</g,"<").replace(/>/g,">"); return this;}; this.underscorize = function(){this.s = this.s.replace(/ /g,"_"); return this;}; this.dasherize = function(){this.s = this.s.replace(/ /g,"-"); return this;}; this.spacify = function(){this.s = this.s.replace(/_/g," "); return this;}; this.left = function(length){this.s = this.s.substring(length,0); return this;}; this.right = function(length){this.s = this.s.substring(this.s.length,this.s.length-length); return this;}; this.shorten = function(length){if(this.s.length<=length){return this.s;}else{this.left(this.s,length)+"..."; return this;}}; this.mid = function(start,length){return this.s.substring(start,(length+start));}; this._down = function(){return this.s;}; // breaks chain, but lets you run core js string functions /******* these functions CANNOT be chained (they do not return the $__STRING__$ object) ******/ this.contains = function(needle){if(this.s.indexOf(needle)!==-1){return true;}else{return false;}}; this.startswith = function(needle){if(this.left(this.s,needle.length)==needle){return true;}else{return false;}}; this.endswith = function(needle){if(this.right(this.s,needle.length)==needle){return true;}else{return false;};}; } function $E(in_string){return new $__STRING__$(in_string);} String.prototype._enhance = function(){return new $__STRING__$(this);}; String.prototype._up = function(){return new $__STRING__$(this);}; It works fairly well, and I can chain commands etc. I set it up so I can cast a string as an enhanced string these 2 ways: $E('some string'); 'some string'._enhance(); However, each time I want to use a built-in string method, I need to convert it back to a string first. So for now, I put in _down() and _up() methods like so: alert( $E("hello man").uppercase()._down().replace("N", "Y")._up().dasherize() ); alert( "hello man"._enhance().uppercase()._down().replace("N", "Y")._up().dasherize() ); It works fine, but what I really want to do it be able to use all of the built-in functions a string can use. I realize I can just replicate each function inside my object, but I was hoping there was a simpler way. So question is, is there an easy way to do that? Thanks -

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  • Haskell: monadic takeWhile?

    - by Mark Rushakoff
    I have some functions written in C that I call from Haskell. These functions return IO (CInt). Sometimes I want to run all of the functions regardless of what any of them return, and this is easy. For sake of example code, this is the general idea of what's happening currently: Prelude> let f x = print x >> return x Prelude> mapM_ f [0..5] 0 1 2 3 4 5 Prelude> I get my desired side effects, and I don't care about the results. But now I need to stop execution immediately after the first item that doesn't return my desired result. Let's say a return value of 4 or higher requires execution to stop - then what I want to do is this: Prelude> takeWhile (<4) $ mapM f [0..5] Which gives me this error: <interactive:1:22: Couldn't match expected type `[b]' against inferred type `IO a' In the first argument of `mapM', namely `f' In the second argument of `($)', namely `mapM f ([0 .. 5])' In the expression: takeWhile (< 4) $ mapM f ([0 .. 5]) And that makes sense to me - the result is still contained in the IO monad, and I can't just compare two values contained in the IO monad. I know this is precisely the purpose of monads -- chaining results together and discarding operations when a certain condition is met -- but is there an easy way to "wrap up" the IO monad in this case to stop executing the chain upon a condition of my choosing, without writing an instance of MonadPlus? Can I just "unlift" the values from f, for the purposes of the takeWhile? Is this a solution where functors fit? Functors haven't "clicked" with me yet, but I sort of have the impression that this might be a good situation to use them. Update: @sth has the closest answer to what I want - in fact, that's almost exactly what I was going for, but I'd still like to see whether there is a standard solution that isn't explicitly recursive -- this is Haskell, after all! Looking back on how I worded my question, now I can see that I wasn't clear enough about my desired behavior. The f function I used above for an example was merely an example. The real functions are written in C and used exclusively for their side effects. I can't use @Tom's suggestion of mapM_ f (takeWhile (&lt;4) [0..5]) because I have no idea whether any input will really result in success or failure until executed. I don't actually care about the returned list, either -- I just want to call the C functions until either the list is exhausted or the first C function returns a failure code. In C-style pseudocode, my behavior would be: do { result = function_with_side_effects(input_list[index++]); } while (result == success && index < max_index); So again, @sth's answer performs the exact behavior that I want, except that the results may (should?) be discarded. A dropWhileM_ function would be equivalent for my purposes. Why isn't there a function like that or takeWhileM_ in Control.Monad? I see that there was a similar discussion on a mailing list, but it appears that nothing has come of that.

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  • map with string is broken?[solved]

    - by teritriano
    Yes. I can't see what im doing wrong the map is string, int Here the method bange::function::Add(lua_State *vm){ //userdata, function if (!lua_isfunction(vm, 2)){ cout << "bange: AddFunction: First argument isn't a function." << endl; return false;} void *pfunction = const_cast<void *>(lua_topointer(vm, 2)); char key[32] = {0}; snprintf(key, 32, "%p", pfunction); cout << "Key: " << key << endl; string strkey = key; if (this->functions.find(strkey) != this->functions.end()){ luaL_unref(vm, LUA_REGISTRYINDEX, this->functions[strkey]);} this->functions[strkey] = luaL_ref(vm, LUA_REGISTRYINDEX); return true; Ok, when the code is executed... Program received signal SIGSEGV, Segmentation fault. 0x00007ffff6e6caa9 in std::basic_string<char, std::char_traits<char>, std::allocator<char> > ::compare(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) const () from /usr/lib/libstdc++.so.6 Seriously, what's wrong with my code. Thanks for help. Edit 1: Ok, I've done the solution and still fails. I've tried directly insert a string but gives the same error. Let's see, the object is a bange::scene inherited from bange::function. I create the object with lua_newuserdata: bange::scene *scene = static_cast<bange::scene *>(lua_newuserdata(vm, sizeof(bange::scene))); (...) scene = new (scene) bange::scene(width, height, nlayers, vm); I need this for LUA garbage collection. Now the access to bange::function::Add from Lua: static int bangefunction_Add(lua_State *vm){ //userdata, function bange::function *function = reinterpret_cast<bange::function *>(lua_touserdata(vm, 1)); cout &lt&lt "object with bange::function: " &lt&lt function << endl; bool added = function->bange::function::Add(vm); lua_pushboolean(vm, static_cast<int>(added)); return 1; } Userdata is bange::scene stored in Lua. Knowing that userdata is scene, in fact, the object's direction is the same when I've created the scene before. I need the reinterpret_cast, and then call the method. The pointer "this" is still the same direction inside the method. solved I did a small test in the bange::function constructor which works without problems. bange::function::function(){ string test("test"); this->functions["test"] = 2; } I finally noticed that the problem is bange::function *function = reinterpret_cast<bange::function *>(lua_touserdata(vm, 1)); because the object is bange::scene and no bange::function (i admit it, a pointer corruption) and this seems more a code design issue. So this, in a way, is solved. Thanks everybody.

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  • PostgreSQL lots of large Arrays and Writes

    - by strife911
    Hi, I am running a python program that spawns 8 threads and as each thread launch its own postmaster process via psycopg2. This is to maximize the use of my CPU-cores (8). Each thread call a series of SQL Functions. Most of these functions go through many thousands of rows each associated to a large FLOAT8[] Array (250-300) values by using unnest() and multiplying each FLOAT8 by an another FLOAT8 associated to each row. This Array approach minimized the size of the Indexes and the Tables. The Function ends with an Insert into another Table of a row of the same form (pk INT4, array FLOAT8[]). Some SQL Functions called by python will Update a row of these kind of Tables (with large Arrays). Now I currently have configured PostgreSQL to use most of the memory for cache (effective_cache_size of 57 GB I think) and only a small amount of it for shared memory (1GB I think). First, I was wondering what the difference between Cache and Shared memory was in regards to PostgreSQL (and my application). What I have noticed is that only about 20-40% of my total CPU processing power is used during the most Read intensive parts of the application (Select unnest(array) etc). So secondly, I was wondering what I could do to improve this so that 100% of the CPU is used. Based on my observations, it does not seem to have anything to do with python or its GIL. Thanks

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