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  • Haskell function composition (.) and function application ($) idioms: correct use.

    - by Robert Massaioli
    I have been reading Real World Haskell and I am nearing the end but a matter of style has been niggling at me to do with the (.) and ($) operators. When you write a function that is a composition of other functions you write it like: f = g . h But when you apply something to the end of those functions I write it like this: k = a $ b $ c $ value But the book would write it like this: k = a . b . c $ value Now to me they look functionally equivalent, they do the exact same thing in my eyes. However, the more I look, the more I see people writing their functions in the manner that the book does: compose with (.) first and then only at the end use ($) to append a value to evaluate the lot (nobody does it with many dollar compositions). Is there a reason for using the books way that is much better than using all ($) symbols? Or is there some best practice here that I am not getting? Or is it superfluous and I shouldn't be worrying about it at all? Thanks.

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  • Extend legacy site with another server-side programming platform best practice

    - by Andrew Florko
    Company I work for have a site developed 6-8 years ago by a team that was enthusiastic enough to use their own private PHP-based CMS. I have to put dynamic data from one intranet company database on this site in one week: 2-3 pages. I contacted company site administrator and she showed me administrative part - CMS allows only to insert html blocks & manage site map (site is deployed on machine that is inside company & fully accessible & upgradeable). I'm not a PHP-guy & I don't want to dive into legacy hardly-who-ever-heard-about CMS engine I also don't want to contact developers team, 'cos I'm not sure they are still present and capable enough to extend this old days site and it'll take too much time anyway. I am about to deploy helper asp.net site on IIS with 2-3 pages required & refer helper site via iframe from present site. New pages will allow to download some dynamic content from present site also. Is it ok and what are the pitfalls with iframe approach?

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  • Where to put a recursive function when following MVC?

    - by Glibly
    Hello, I have a recursive function being used to generate a menu on my site. The function is calling a database for each level of children in the menu, and generating html for them. I've currently put this function in a Model part of the code, however, I feel that generating html in the model goes against the MVC. I didn't put it in a Controller because I didn't want to have database calls or HTML generation there. I didn't put it in a View because I didn't want database calls there either. Is the 'correct' way of tackling this problem to have a Controller call a recursive function in a Model that returns a 2d array representing the menu. Then pass the array to a view which has it's own recursive function for generating html from the array?

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  • Is concatenating with an empty string to do a string conversion really that bad?

    - by polygenelubricants
    Let's say I have two char variables, and later on I want to concatenate them into a string. This is how I would do it: char c1, c2; // ... String s = "" + c1 + c2; I've seen people who say that the "" + "trick" is "ugly", etc, and that you should use String.valueOf or Character.toString instead. I prefer this construct because: I prefer using language feature instead of API call if possible In general, isn't the language usually more stable than the API? If language feature only hides API call, then even stronger reason to prefer it! More abstract! Hiding is good! I like that the c1 and c2 are visually on the same level String.valueOf(c1) + c2 suggests something is special about c1 It's shorter. Is there really a good argument why String.valueOf or Character.toString is preferrable to "" +? Trivia: in java.lang.AssertionError, the following line appears 7 times, each with a different type: this("" + detailMessage);

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  • When NOT to use MVVM?

    - by Vitalij
    I have started using MVVM pattern recently. I have had several projects where I used it and with every new one, I start to see that it will fit great within that new project. And now I start to ask myself are there situation when it's better NOT to use MVVM. Or is it such a nice pattern which you can use anywhere? Could you please describe several scenarios where MVVM wouldn't be the best choice?

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  • Best ways to reuse Java methods

    - by carillonator
    I'm learning Java and OOP, and have been doing the problems at Project Euler for practice (awesome site btw). I find myself doing many of the same things over and over, like: checking if an integer is prime/generating primes generating the Fibonacci series checking if a number is a palindrome What is the best way to store and call these methods? Should I write a utility class and then import it? If so, do I import a .class file or the .java source? I'm working from a plain text editor and the Mac terminal. Thanks!

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  • design pattern for related inputs

    - by curiousMo
    My question is a design question : let's say i have a data entry web page with 4 drop down lists, each depending on the previous one, and a bunch of text boxes. ddlCountry (DropDownList) ddlState (DropDownList) ddlCity (DropDownList) ddlBoro (DropDownList) txtAddress (TxtBox) txtZipcode(TxtBox) and an object that represents a datarow with a value for each: countrySeqid stateSeqid citySeqid boroSeqid address zipCode naturally the country, state, city and boro values will be values of primary keys of some lookup tables. when the user chooses to edits that record, i would load it from database and load it into the page. the issue that I have is how to streamline loading the DropDownLists. i have some code that would grab the object,look thru its values and move them to their corresponding input controls in one shot. but in this case i will have to load the ddlCountry with possible values, then assign values, then do the same thing for the rest of the ddls. I guess i am looking for an elegant solution. i am using asp.net, but i think it is irrelevant to the question. i am looking more into a design pattern.

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  • How can I determine/use $(this) in js callback script

    - by Rabbott
    I am using Rails and jQuery, making an ajax call initiated by clicking a link. I setup my application.js file to look like the one proposed here and it works great. The problem I'm having is how can I use $(this) in my say.. update.js.erb file to represent the link I clicked? I don't want to have to assign an ID to every one, then recompile that id in the callback script.. EDIT To give a simple example of something similar to what I'm trying to do (and much easier to explain): If a user clicks on a link, that deletes that element from a list, the controller would handle the callback, and the callback (which is in question here) would delete the element I clicked on, so in the callback delete.js.erb would just say $(this).fadeOut(); This is why I want to use $(this) so that I dont have to assign an ID to every element (which would be the end of the world, just more verbose markup) application.js jQuery.ajaxSetup({ 'beforeSend': function(xhr) {xhr.setRequestHeader("Accept", "text/javascript,application/javascript,text/html")} }) function _ajax_request(url, data, callback, type, method) { if (jQuery.isFunction(data)) { callback = data; data = {}; } return jQuery.ajax({ type: method, url: url, data: data, success: callback, dataType: type }); } jQuery.extend({ put: function(url, data, callback, type) { return _ajax_request(url, data, callback, type, 'PUT'); }, delete_: function(url, data, callback, type) { return _ajax_request(url, data, callback, type, 'DELETE'); } }); jQuery.fn.submitWithAjax = function() { this.unbind('submit', false); this.submit(function() { $.post(this.action, $(this).serialize(), null, "script"); return false; }) return this; }; // Send data via get if <acronym title="JavaScript">JS</acronym> enabled jQuery.fn.getWithAjax = function() { this.unbind('click', false); this.click(function() { $.get($(this).attr("href"), $(this).serialize(), null, "script"); return false; }) return this; }; // Send data via Post if <acronym title="JavaScript">JS</acronym> enabled jQuery.fn.postWithAjax = function() { this.unbind('click', false); this.click(function() { $.post($(this).attr("href"), $(this).serialize(), null, "script"); return false; }) return this; }; jQuery.fn.putWithAjax = function() { this.unbind('click', false); this.click(function() { $.put($(this).attr("href"), $(this).serialize(), null, "script"); return false; }) return this; }; jQuery.fn.deleteWithAjax = function() { this.removeAttr('onclick'); this.unbind('click', false); this.click(function() { $.delete_($(this).attr("href"), $(this).serialize(), null, "script"); return false; }) return this; }; // This will "ajaxify" the links function ajaxLinks(){ $('.ajaxForm').submitWithAjax(); $('a.get').getWithAjax(); $('a.post').postWithAjax(); $('a.put').putWithAjax(); $('a.delete').deleteWithAjax(); } show.html.erb <%= link_to 'Link Title', article_path(a, :sentiment => Article::Sentiment['Neutral']), :class => 'put' %> The combination of the two things will call update.js.erb in rails, the code in that file is used as the callback of the ajax ($.put in this case) update.js.erb // user feedback $("#notice").html('<%= flash[:notice] %>'); // update the background color $(this OR e.target).attr("color", "red");

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  • What types of objects should the ViewModel reference in the MVVM pattern?

    - by Blanthor
    I've seen quite a few examples of MVVM. I can see that the View should reference the ViewModel. I've seen recently an example of a ViewModel referencing a View, which seems wrong to me, as it would result in tighter coupling. Given that ViewModel is often described as an intermediary between the View and the Model, is there more to the ViewModel than a facade to domain objects? I hope I used the term "facade" correctly here.

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  • How to handle recurring execution?

    - by ShaneC
    I am trying to validate the solution I came up for what I think is a fairly typical problem. I have a service running and every 10 minutes it should do something. I've ended up with the following: private bool isRunning = true; public void Execute() { while(isRunning) { if(isRunning) { DoSomething(); m_AutoResetEvent.WaitOne(new Timespan(0, 10, 0)); } } } public void Stop() { isRunning = false; m_AutoResetEvent.Set(); } The immediate potential problems I can see is that I'm not doing any sort of locking around the isRunning modification in Stop() which gets called by another thread but I'm not sure I really need to? The worst that I think could happen is that it runs one extra cycle. Beyond that are there any obvious problems with this code? Is there a better way to solve this problem that I'm unaware of?

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  • Right design to validate attributes of a class instance

    - by systempuntoout
    Having a simple Python class like this: class Spam(object): __init__(self, description, value): self.description = description self.value = value Which is the correct approach to check these constraints: "description cannot be empty" "value must be greater than zero" Should i: 1.validate data before creating spam object ? 2.check data on __init__ method ? 3.create an is_valid method on Spam class and call it with spam.isValid() ? 4.create an is_valid static method on Spam class and call it with Spam.isValid(description, value) ? 5.check data on setters? 6.... Could you recommend a well designed\Pythonic\not verbose (on class with many attributes)\elegant approach?

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  • What is the MVC version of this code?

    - by Ian Boyd
    i'm trying to wrap my head around how to enterprise up my code: taking a simple routine and splitting it up into 5 or 6 methods in 3 or 4 classes. i quickly came up three simple examples of code how i currently write it. Could someone please convert these into an MVC/MVP obfuscated version? Example 1: The last name is mandatory. Color the text box red if nothing is entered. Color it green if stuff is entered: private void txtLastname_TextChanged(object sender, EventArgs e) { //Lastname mandatory. //Color pinkish if nothing entered. Greenish if entered. if (txtLastname.Text.Trim() == "") { //Lastname is required, color pinkish txtLastname.BackColor = ControlBad; } else { //Lastname entered, remove the coloring txtLastname.BackColor = ControlGood; } } Example 2: The first name is optional, but try to get it. We'll add a bluish tint to this "try to get" field: private void txtFirstname_TextChanged(object sender, EventArgs e) { //Firstname can be blank. //Hint them that they should *try* to get it with a bluish color. //If they do enter stuff: it better be not all spaces. if (txtFirstname.Text == "") { //Nothing there, hint it blue txtFirstname.BackColor = ControlRequired; } else if (txtFirstname.Text.Trim() == "") { //They entered spaces - bad user! txtFirstname.BackColor = ControlBad; } else { //Entered stuff, remove coloring txtFirstname.BackColor = SystemColors.Window; } } Example 3 The age is totally optional. If an age is entered, it better be valid: private void txtAge_TextChanged(object sender, EventArgs e) { //Age is optional, but if entered it better be valid int nAge = 0; if (Int32.TryParse(txtAge.Text, out nAge)) { //Valid integer entered if (nAge < 0) { //Negative age? i don't think so txtAge.BackColor = ControlBad; } else { //Valid age entered, remove coloring txtAge.BackColor = SystemColors.Window; } } else { //Whatever is in there: it's *not* a valid integer, if (txtAge.Text == "") { //Blank is okay txtAge.BackColor = SystemColors.Window; } else { //Not a valid age, bad user txtAge.BackColor = ControlBad; } } } Every time i see MVC code, it looks almost like random splitting of code into different methods, classes, and files. i've not been able to determine a reason or pattern to their madness. Without any understanding of they why it's being one some way, it makes no sense. And using the words model, view, controller and presenter, like i'm supposed to know what that means, doesn't help. The model is your data. The view shows data on screen. The controller is used to carry out the users actions And oranges taste orangy. Here's my attempt at splitting things up in order to make the code more difficult to follow. Is this anywhere close to MVC? private void txtFirstname_TextChanged(object sender, EventArgs e) { FirstnameTextChangedHandler(sender, e); } private void FirstnameTextChangedHandler(sender, e) { string firstname = GetFirstname(); Color firstnameTextBoxColor = GetFirstnameTextBoxColor(firstname); SetFirstNameTextBoxColor(firstnameTextBoxColor); } private string GetFirstname() { return txtFirstname.Text; } private Color GetFirstnameTextBoxColor(string firstname) { //Firstname can be blank. //Hint them that they should *try* to get it with a bluish color. //If they do enter stuff: it better be not all spaces. if (firstname == "") { //Nothing there, hint it blue return GetControlRequiredColor(); } else if (firstname.Trim() == "") { //They entered spaces - bad user! return GetControlBadColor(); } else { //Entered stuff, remove coloring return GetControlDefaultColor(); } } private Color GetControlRequiredColor() { return ControlRequired; } private Color GetControlBadColor() { return ControlBad; } private Color GetControlGoodColor() { return ControlGood; } //am i doin it rite i've obfuscated the code, but it's still altogether. The next step in the MVC obfuscation, i gather, is to hide the code in 3 or 4 different files. It's that next step that i don't understand. What is the logical separation of which functions are moved into what other classes? Can someone translate my 3 simple examples above into full fledged MVC obfuscation? Edit: Not ASP/ASP.NET/Online. Pretend it's on a desktop, handheld, surface, kiosk. And pretend it's language agnostic.

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  • Buffering db inserts in multithreaded program

    - by Winter
    I have a system which breaks a large taks into small tasks using about 30 threads as a time. As each individual thread finishes it persists its calculated results to the database. What I want to achieve is to have each thread pass its results to a new persisance class that will perform a type of double buffering and data persistance while running in its own thread. For example, after 100 threads have moved their data to the buffer the persistance class then the persistance class swaps the buffers and persists all 100 entries to the database. This would allow utilization of prepared statements and thus cut way down on the I/O between the program and the database. Is there a pattern or good example of this type of multithreading double buffering?

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  • Pitfalls when switching to .NET for Windows CE?

    - by Presidenten
    Hi! I have been developing in .NET for quite some time now. But now I have customer who wants me to develop an application for them in .NET for Windows CE. I have done some embedded system programming in C before, but never in .NET. Please share any tips or tricks that would make my life easier when taking this assignment, or perhaps knowledge about any pitfalls to watch out for.

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  • Command Query Separation validating for retries

    - by Neil Barnwell
    So I'm comfortable with the basic concept of CQS, where you might have a command that writes to one database, and that updates the query database that you read from. However, consider the scenario where you are entering data, and want to prevent duplicates. Using new employee data entry an employee register as an example, working through a pile of application forms to key in the new employees' details: Take top sheet. Key in employee name and unique payroll number to UI. Submit. Put paper in "completed pile". Repeat. How would you now prevent the user from keying in the same payroll number again, say for instance if they get distracted and can't remember whether they've keyed one in already and the "message" hasn't got all the way back to the query db for the user to search?

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  • What are the constraints on Cocoa Framework version numbers?

    - by Joe
    We're distributing a Cocoa framework with regular updates. We'll be updating the version numbers with each release. The Apple documentation appears to suggest that version numbers should be consecutive incrementing integers. We are distributing output in several formats, and the framework is only one of them. We would rather not have to maintain a separate numbering system just for our frameworks. We don't really care about the precise format of the version numbers of the framework, so long as they change whenever the product changes, and behave in a correct and expected manner. I'm looking for a sensible and correct way of avoiding having to run a separate version number counter. One suggestion is that for product version 12.34.56 we could simply remove the dots and say the framework version is 123456. Is there a constraint on the type of number that can be represented (uint? long?) Does it have to be a number? Could it be a string? Do the numbers have to be consecutive? Is there a standard way of doing things in this situation?

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