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  • What is up with the Joy of Clojure 2nd edition?

    - by kurofune
    Manning just released the second edition of the beloved Joy of Clojure book, and while I share that love I get the feeling that many of the examples are already outdated. In particular, in the chapter on optimization the recommended type-hinting seems not to be allowed by the compiler. I don't know if this was allowable for older versions of Clojure. For example: (defn factorial-f [^long original-x] (loop [x original-x, acc 1] (if (>= 1 x) acc (recur (dec x) (*' x acc))))) returns: clojure.lang.Compiler$CompilerException: java.lang.UnsupportedOperationException: Can't type hint a primitive local, compiling:(null:3:1) Likewise, the chapter on core.logic seems be using an old API and I have to find workarounds for each example to accommodate the recent changes. For example, I had to turn this: (logic/defrel orbits orbital body) (logic/fact orbits :mercury :sun) (logic/fact orbits :venus :sun) (logic/fact orbits :earth :sun) (logic/fact orbits :mars :sun) (logic/fact orbits :jupiter :sun) (logic/fact orbits :saturn :sun) (logic/fact orbits :uranus :sun) (logic/fact orbits :neptune :sun) (logic/run* [q] (logic/fresh [orbital body] (orbits orbital body) (logic/== q orbital))) into this, leveraging the pldb lib: (pldb/db-rel orbits orbital body) (def facts (pldb/db [orbits :mercury :sun] [orbits :venus :sun] [orbits :earth :sun] [orbits :mars :sun] [orbits :jupiter :sun] [orbits :saturn :sun] [orbits :uranus :sun] [orbits :neptune :sun])) (pldb/with-db facts (logic/run* [q] (logic/fresh [orbital body] (orbits orbital body) (logic/== q orbital)))) I am still pulling teeth to get the later examples to work. I am relatively new programming, myself, so I wonder if I am naively looking over something here, or are if these points I'm making legitimate concerns? I really want to get good at this stuff like type-hinting and core.logic, but wanna make sure I am studying up to date materials. Any illuminating facts to help clear up my confusion would be most welcome.

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  • Rails: How to toggle a boolean field from a view?

    - by sscirrus
    Very simple question. I have a boolean field called "saved" in my database. I want to toggle this field by clicking on a text link that changes from "Save" to "Unsave" depending on the situation, and updates my "Customer" table with 0 or 1. I imagine Javascript may be a way to go for this but I am not experienced enough (yet!) in Javascript to know how to code it. What is the best way to approach this problem, and how can I find the code I would need to drop into my view to make this toggle work? Thank you very much.

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  • In PHP can I check a boolean on a function call?

    - by Chris
    I have a function which checks the passed value and returns false or true, if false I want it to add something to an array. The code I've written is below. if(!check_input($_POST['username'])){ $errors[] = "Username"; } Right now it adds to my array anyway, regardless of what is entered in the form. Is the way I've written that the correct way to check if the return from check_input() is false? I've checked the function's logic by altering the returns to echoes and it's returning the correct value, I'm just not sure if I'm checking it wrong. I'd previously attempted to write it as $X=check_input etc, and then if(check_value == false) but that doesn't seem to give me the desired result either. Hmmm a quick pointer please!

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  • how to write good programming logic?

    - by user106616
    recently I got job as a java developer, and now I have assigned project too. I want to know what is a good logic? when I check in the code my team lead is saying that its a good code. But when it comes to my project manager he is saying that its a bad code. And he is changing my code, after his changes if I see his code its really very very good and even simple. can you please tell me how to develop the good program, good logic? what is the best way to structure a problem in terms of code?

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  • Are There Realistic/Useful Solutions for Source Control for Ladder Logic Programs

    - by Steven A. Lowe
    Version control for ladder logic (LL) programs for programmable logic controllers (PLCs) seems to be virtually non-existent. It may be because LL is a visual language and tends to be stored in binary files, or it may be because source code control hasn't "caught on" in process control engineering circles - or perhaps my Google-Fu is weak tonight. Do you know of any realistic and useful solutions for version control for such systems? Definitions: realistic = changes to the programs are tracked by user and subject to reversion and merges useful = the system integrates with visual LL designers, is not limited to LL from a single PLC manufacturer, and does not cost a ridiculous amount of money? Note: I have heard of people using SVN or Mercurial et al to track the binary files, but I don't think the diff/merge capabilities would display readable differences.

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  • Which game logic should run when doing prediction for PNP state updates

    - by spaceOwl
    We are writing a multiplayer game, where each game client (player) is responsible for sending state updates regarding its "owned" objects to other players. Each message that arrives to other (remote) clients is processed as such: Figure out when the message was sent. Create a diff between NOW and that time. Run game specific logic to bring the received state to "current" time. I am wondering which sort of logic should execute as part of step #3 ? Our game is composed of a physical update (position, speed, acceleration, etc) and many other components that can update an object's state and occur regularly (locally). There's a trade off here - Getting the new state quickly or remaining "faithful" to the true state representation and executing the whole thing to predict the "true" state when receiving state updates from remote clients. Which one is recommended to be used? and why?

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  • Splitting Logic, Data, Layout and "Hacks"

    - by fjdumont
    Sure, we all heard of programming patterns such as MVVM, MVC and such. But that isn't really what I'm looking into as Layout, Data and Logic is already pretty much split up (XML-Layout markup, Database, insert your language of choice here). The platform I am developing for is hard to maintain over the updated versions and older OSes. The project significantly grew up over the last few months and dealing with different platform versions really is a pain. For example simply disabling an user interface control for all existing versions took me around 40 lines of code in the logic layer, wrangling around with invocation, delegation, singletons that provide UI handling and so on. Is there a clean way to keep track of those "hacks" by maybe excluding it into separate classes or even packages? Should I overwrite existing framework code in order to handle my requirements correctly? If so, does that concept have a name?

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  • Better solution for boolean mixing?

    - by Ruben Nunez
    Sorry if this question has been asked in the past, but searching Google and here didn't yield relevant results, so here goes. I'm working on a fragment shader that implements both conditional/boolean diffuse and bump mapping (that is to say, you don't need a diffuse texture or a normals texture, and if they're not present, they're simply changed to default values). My current solution is to use a uniform float to say "mix amount". For example, computing the diffuse texel works as: // Compute diffuse amount scaled by vCol // If no texture is present (mDif = 0.0), then DiffuseTexel = vCol // kT[0] is the diffuse texture // vTex is the texture co-ordinates // mDif is the uniform float containing the mix amount (either 0.0 or 1.0) vec4 DiffuseTexel = vCol*mix(vec4(1.0), texture2D(kT[0], vTex), mDif); While that works great and all, I was wondering if there's a better way of doing this, as I will never have any use for in-between values for funky effects. I know that perhaps the best solution is to simply write separate shaders for mDif=0.0 and mDif=1.0, but I'd like a more elegant solution than splicing shaders before compiling or writing multiple shader files and keeping each one updated. Any ideas are greatly appreciated. =)

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  • Update Boolean attributes from another controller

    - by sidonstackoverflow
    I have Users controller and session controller . I want to update one user attribute from session controller . How can i do that ?? I am currently using rails 4.0 . Users controller: class UsersController < ApplicationController def show if Spec.find_by_user_id params[:id] @user = User.find(params[:id]) @spec = Spec.find_by_user_id params[:id] else if params[:id] == session[:id] redirect_to spec_edit_path(params[:id]) else redirect_to(community_index_path, {:notice => "Sorry there was an error"}) end end end def index end def new @user = User.new end def create @user = User.new(user_params) if @user.save flash[:success] = "Welcome buddy !" redirect_to @user else render 'new' end end private def user_params params.require(:user).permit(:name, :email, :password, :password_confirmation) end end Sessions Controller : class SessionsController < ApplicationController def new end def create user = User.find_by(email: params[:session][:email]) if user && user.authenticate(params[:session][:password]) session[:user_id] = user.id User.update(user.status, 'true') redirect_to root_url, :notice => 'You successfully logged in ' else flash.now[:error] = 'Invalid email/password combination' # Not quite right! render 'new' end end def destroy session[:user_id] = nil redirect_to root_url, :notice => 'You successfully logged out ' end end In above code when User logged in i just want to update my boolean column status at users table from sessions controller , but i failed . I am thankful to whom would like to answer my question !

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  • Should programmers use boolean variables to "document" their code?

    - by froadie
    I'm reading McConell's Code Complete, and he discusses using boolean variables to document your code. For example, instead of: if((elementIndex < 0) || (MAX_ELEMENTS < elementIndex) || (elementIndex == lastElementIndex)){ ... } He suggests: finished = ((elementIndex < 0) || (MAX_ELEMENTS < elementIndex)); repeatedEntry = (elementIndex == lastElementIndex); if(finished || repeatedEntry){ ... } This strikes me as logical, good practice, and very self-documenting. However, I'm hesitant to start using this technique regularly as I've almost never come across it; and perhaps it would be confusing just by virtue of being rare. However, my experience is not very vast yet, so I'm interested in hearing programmers' opinion of this technique, and I'd be curious to know if anyone uses this technique regularly or has seen it often when reading code. Is this a worthwhile convention/style/technique to adopt? Will other programmers understand and appreciate it, or consider it strange?

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  • What's the right way to handle "One, Both, or None" logic?

    - by Stephen
    I have a logic situation that is best described as two "Teams" trying to win a task. The outcome of this task could be a single winner, a tie (draw), or no winner (stalemate). Currently, I'm using a nested if/else statement like so: // using PHP, but the concept seems language agnostic. if ($team_a->win()) { if ($team_b->win()) { // this is a draw } else { // team_a is the winner } } else { if ($team_b->win()) { // team_b is the winner } else { // This is a stalemate, no winner. } } This seems rather spaghetti-like and repetitive. Is there a more logical, DRY pattern I could use?

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  • How should I design a correct OO design in case of a Business-logic wide operation

    - by Mithir
    EDIT: Maybe I should ask the question in a different way. in light of ammoQ's comment, I realize that I've done something like suggested which is kind of a fix and it is fine by me. But I still want to learn for the future, so that if I develop new code for operations similar to this, I can design it correctly from the start. So, if I got the following characteristics: The relevant input is composed from data which is connected to several different business objects All the input data is validated and cross-checked Attempts are made in order to insert the data to the DB All this is just a single operation from Business side prospective, meaning all of the cross checking and validations are just side effects. I can't think of any other way but some sort of Operator/Coordinator kind of Object which activates the entire procedure, but then I fall into a Functional-Decomposition kind of code. so is there a better way in doing this? Original Question In our system we have many complex operations which involve many validations and DB activities. One of the main Business functionality could have been designed better. In short, there were no separation of layers, and the code would only work from the scenario in which it was first designed at, and now there were more scenarios (like requests from an API or from other devices) So I had to redesign. I found myself moving all the DB code to objects which acts like Business to DB objects, and I've put all the business logic in an Operator kind of a class, which I've implemented like this: First, I created an object which will hold all the information needed for the operation let's call it InformationObject. Then I created an OperatorObject which will take the InformationObject as a parameter and act on it. The OperatorObject should activate different objects and validate or check for existence or any scenario in which the business logic is compromised and then make the operation according to the information on the InformationObject. So my question is - Is this kind of implementation correct? PS, this Operator only works on a single Business-wise Operation.

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  • Designing binary operations(AND, OR, NOT) in graphs DB's like neo4j

    - by Nicholas
    I'm trying to create a recipe website using a graph database, specifically neo4j using spring-data-neo4j, to try and see what can be done in Graph Databases. My model so far is: (Chef)-[HAS_INGREDIENT]->(Ingredient) (Chef)-[HAS_VALUE]->(Value) (Ingredient)-[HAS_INGREDIENT_VALUE]->(Value) (Recipe)-[REQUIRES_INGREDIENT]->(Ingredient) (Recipe)-[REQUIRES_VALUE]->(Value) I have this set up so I can do things like have the "chef" enter ingredients they have on hand, and suggest recipes, as well as suggest recipes that are close matches, but missing one ingredient. Some recipes can get complex, utilizing AND, OR, and NOT type logic, something like (Milk AND (Butter OR spread OR (vegetable oil OR olive oil))) and I'm wondering if it would be sane to model this in a graph using a tree type representation? An example of what I was thinking is to create three "node" types of AND, OR, and NOT and have each of them connect to the nodes value underneath. How else might this be represented in a Graph Database or is my example above a decent representation?

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  • looking for a short explanation of fuzzy logic

    - by user613326
    Well i got the idea that basics of fuzzy logic are not that hard to grasp. And i got the feeling that someone might explain it to me in like 30 minutes. Just like i understand neural networks and am able to re-create the famous Xor problem. And go just beyond it and create 3 layer networks of x nodes. I'd like to understand fuzzy till a similar usefully level, in c# language. However the problem is face, I'd like to get concept right however i see many websites who include lots of errors in their basic explaining. Like for example showing pictures and use different numbers as shown in pictures to calculate, as if lots of people just copied stuff without noticing what they write down. While others for me go to deep in their math notation) To me that's very annoying to learn from. For me there is no need to re-invent wheel; Aforge already got a fuzzy logic framework. So what i am looking for are some good examples, good examples like how the neural XOR problem is solved. Is there anyone such a instructional resource out there; do you know a web page, or YouTube where it is shortly explained, what would you recommend me ? Note this article comes close; but it just doesnt nail it for me. After that i downloaded a bunch of free PDF's but most are academic and hard to read for me (i'm not English and dont have a special math degree). (i've been looking around a lot for this, good starter material about it is hard to find).

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  • Documenting mathematical logic in code

    - by Kiril Raychev
    Sometimes, although not often, I have to include math logic in my code. The concepts used are mostly very simple, but the resulting code is not - a lot of variables with unclear purpose, and some operations with not so obvious intent. I don't mean that the code is unreadable or unmaintainable, just that it's waaaay harder to understand than the actual math problem. I try to comment the parts which are hardest to understand, but there is the same problem as in just coding them - text does not have the expressive power of math. I am looking for a more efficient and easy to understand way of explaining the logic behind some of the complex code, preferably in the code itself. I have considered TeX - writing the documentation and generating it separately from the code. But then I'd have to learn TeX, and the documentation will not be in the code itself. Another thing I thought of is taking a picture of the mathematical notations, equations and diagrams written on paper/whiteboard, and including it in javadoc. Is there a simpler and clearer way? P.S. Giving descriptive names(timeOfFirstEvent instead of t1) to the variables actually makes the code more verbose and even harder too read.

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  • Is it bad to explicitly compare against boolean constants e.g. if (b == false) in Java?

    - by polygenelubricants
    Is it bad to write: if (b == false) //... while (b != true) //... Is it always better to instead write: if (!b) //... while (!b) //... Presumably there is no difference in performance (or is there?), but how do you weigh the explicitness, the conciseness, the clarity, the readability, etc between the two? Note: the variable name b is just used as an example, ala foo and bar.

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  • Why is the Objective-C Boolean data type defined as a signed char?

    - by EddieCatflap
    Something that has piqued my interest is Objective-C's BOOL type definition. Why is it defined as a signed char (which could cause unexpected behaviour if a value greater than 1 byte in length is assigned to it) rather than as an int, as C does (much less margin for error: a zero value is false, a non-zero value is true)? The only reason I can think of is the Objective-C designers micro-optimising storage because the char will use less memory than the int. Please can someone enlighten me?

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  • Why do Java and C# not have implicit conversions to boolean?

    - by Shaun
    Since I started Java it's been very aggravating for me that it doesn't support implicit conversions from numeric types to booleans, so you can't do things like: if (flags & 0x80) { ... } instead you have to go through this lunacy: if ((flags & 0x80) != 0) { ... } It's the same with null and objects. Every other C-like language I know including JavaScript allows it, so I thought Java was just moronic, but I've just discovered that C# is the same (at least for numbers, don't know about null/objects): http://msdn.microsoft.com/en-us/library/c8f5xwh7(VS.71).aspx Microsoft changed it on purpose from C++, so why? Clearly I'm missing something. Why change (what I thought was) the most natural thing in the world to make it longer to type? What on Earth is wrong with it?

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  • Forcing value to boolean: (bool) makes warning, !! doesnt.

    - by Newbie
    I like (bool) way more, but it generates warnings. How do i get rid off the warnings? I have code like: bool something_else = 0; void switcher(int val = -1){ if(val != -1){ something_else = (bool)val; }else{ something_else ^= 1; } } Should i just do it like everyone else and use '!!' or make it somehow hide the warning messages when using (bool) ? Or is '!!' actually faster than (bool) ? I would like to use (bool) and so i have to hide the warning, but how?

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