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Search found 12 results on 1 pages for 'thurn'.

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• Why does Google's closure library not use real private members?

  - by Thor Thurn

  I've been a JavaScript developer for a while now, and I've always thought that the correct way to implement private members in JavaScript is to use the technique outlined by Doug Crockford here: http://javascript.crockford.com/private.html. I didn't think this was a particularly controversial piece of JavaScript wisdom, until I started using the Google Closure library. Imagine my surprise... the library makes no effort to use Crockford-style information hiding. All they do is use a special naming convention and note "private" members in the documentation. I'm in the habit of assuming that the guys at Google are usually on the leading edge of software quality, so what gives? Is there some downside to following Mr. Crockford's advice that's not obvious?

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• Haskell: convert unicode integer to actual unicode character

  - by Thor Thurn

  Suppose that my Haskell function is given an input, which is supposed to be the number of a unicode code point. How can one convert this to the corresponding character? Example: 0x0123 to '{'.

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• Can Haskell's Parsec library be used to implement a recursive descent parser with backup?

  - by Thor Thurn

  I've been considering using Haskell's Parsec parsing library to parse a subset of Java as a recursive descent parser as an alternative to more traditional parser-generator solutions like Happy. Parsec seems very easy to use, and parse speed is definitely not a factor for me. I'm wondering, though, if it's possible to implement "backup" with Parsec, a technique which finds the correct production to use by trying each one in turn. For a simple example, consider the very start of the JLS Java grammar: Literal: IntegerLiteral FloatingPointLiteral I'd like a way to not have to figure out how I should order these two rules to get the parse to succeed. As it stands, a naive implementation like this: literal = do { x <- try (do { v <- integer; return (IntLiteral v)}) <|> (do { v <- float; return (FPLiteral v)}); return(Literal x) } Will not work... inputs like "15.2" will cause the integer parser to succeed first, and then the whole thing will choke on the "." symbol. In this case, of course, it's obvious that you can solve the problem by re-ordering the two productions. In the general case, though, finding things like this is going to be a nightmare, and it's very likely that I'll miss some cases. Ideally, I'd like a way to have Parsec figure out stuff like this for me. Is this possible, or am I simply trying to do too much with the library? The Parsec documentation claims that it can "parse context-sensitive, infinite look-ahead grammars", so it seems like something like I should be able to do something here.

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• Google Web Toolkit Asynchronous Call from a Service Implementation

  - by Thor Thurn

  I'm writing a simple Google Web Toolkit service which acts as a proxy, which will basically exist to allow the client to make a POST to a different server. The client essentially uses this service to request an HTTP call. The service has only one asynchronous method call, called ajax(), which should just forward the server response. My code for implementing the call looks like this: class ProxyServiceImpl extends RemoteServiceServlet implements ProxyService { @Override public Response ajax(String data) { RequestBuilder rb = /*make a request builder*/ RequestCallback rc = new RequestCallback() { @Override public void onResponseReceived(Response response) { /* Forward this response back to the client as the return value of the ajax method... somehow... */ } }; rb.sendRequest(data, requestCallback); return /* The response above... except I can't */; } } You can see the basic form of my problem, of course. The ajax() method is used asynchronously, but GWT decides to be smart and hide that from the dumb old developer, so they can just write normal Java code without callbacks. GWT services basically just do magic instead of accepting a callback parameter. The trouble arises, then, because GWT is hiding the callback object from me. I'm trying to make my own asynchronous call from the service implementation, but I can't, because GWT services assume that you behave synchronously in service implementations. How can I work around this and make an asynchronous call from my service method implementation?

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• JavaScript Metaprogramming: Reduce boilerplate of adding functions to a function queue

  - by thurn

  I'm working with animation in JavaScript, and I have a bunch of functions you can call to add things to the animation queue. Basically, all of these functions look like this: function foo(arg1, arg2) { _eventQueue.push(function() { // actual logic } } I'm wondering now if it would be possible to cut down on this boilerplate a little bit, though, so I don't need that extra "_eventQueue" line in the function body dozens of times. Would it be possible, for example, to make a helper function which takes an arbitrary function as an argument and returns a new function which is augmented to be automatically added to the event queue? The only problem is that I need to find a way to maintain access to the function's original arguments in this process, which is... complicated.

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• Invoke Haskell function with heterogeneous arguments?

  - by thurn

  I'm currently working on a Haskell project which automatically tests some functions based on an XML specification. The XML specification gives the arguments to each function and the expected result that the function will provide (the arguments are of many different types). I know how to extract the function arguments from the XML and parse them using the read function, but I haven't figured out how to invoke the function using the arguments I get out. What I basically want is to read and store the arguments in a heterogeneous list (my current thinking is to use a list of type Data.Dynamic) and then invoke the function, passing this heterogeneous list as its argument list. Is this possible? Modifying the functions under test is not an option.

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• How do tools like Hiphop for PHP deal with heterogenous arrays?

  - by Derek Thurn

  I think HipHop for PHP is an interesting tool. It essentially converts PHP code into C++ code. Cross compiling in this manner seems like a great idea, but I have to wonder, how do they overcome the fundamental differences between the two type systems? One specific example of my general question is heterogeneous data structures. Statically typed languages don't tend to let you put arbitrary types into an array or other container because they need to be able to figure out the types on the other end. If I have a PHP array like this: $mixedBag = array("cat", 42, 8.5, false); How can this be represented in C++ code? One option would be to use void pointers (or the superior version, boost::any), but then you need to cast when you take stuff back out of the array... and I'm not at all convinced that the type inferencer can always figure out what to cast to at the other end. A better option, perhaps, would be something more like a union (or boost::variant), but then you need to enumerate all possible types at compile time... maybe possible, but certainly messy since arrays can contain arbitrarily complex entities. Does anyone know how HipHop and similar tools which go from a dynamic typing discipline to a static discipline handle these types of problems?

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• Build a JavaScript wrapper for a rails-generated XML API?

  - by Thor Thurn

  I am working with a large website written in Ruby on Rails. Thanks to the support for REST in Rails 2, the site's business logic is all accessible via a consistent XML API. Now I want to be able to easily write one or more JavaScript frontends to the site that interact with the generated Rails XML API. Ideally, an automated wrapper for the API could be created in JavaScript, since this would minimize the effort required in writing XML processing code for the more than 500 API functions. How, then, can I automatically generate a wrapper around a given XML API in JavaScript so that it's more pleasant to work with? I've worked with solutions of this nature for Java that generate classes and methods to wrap an API, so my current thinking is that I want something of that nature for JavaScript. I'd be open to an alternative take on the problem, though.

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• Rails: Check output of path helper from console

  - by Thor Thurn

  Rails defines a bunch of magic with named routes that make helpers for your routes. Sometimes, especially with nested routes, it can get a little confusing to keep track of what URL you'll get for a given route helper method call. Is it possible to, using the Ruby console, see what link a given helper function will generate? For example, given a named helper like post_path(post) I want to see what URL is generated.

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• Ruby: Locate class definition at run time?

  - by Thor Thurn

  I'm having an odd probably with rails right now... a class is being defined somewhere, and I can't find it. Grepping for "class ClassName" hasn't managed to locate it, but it's definitely there when I load up the rails console. It's just a vanilla class inheriting from Object with nothing else defined... quite boring. So, what I'd like is a way to figure out where this class constant was originally defined from the rails console. Something to print out the value of '__ FILE __' when this class was declared, in other words. I feel like some type of metaprogramming should make this possible.

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• typeof === "undefined" vs. != null

  - by Thor Thurn

  I often see JavaScript code which checks for undefined parameters etc. this way: if (typeof input !== "undefined") { // do stuff } This seems kind of wasteful, since it involves both a type lookup and a string comparison, not to mention its verbosity. It's needed because 'undefined' could be renamed, though. My question is: How is that code any better than this approach: if (input != null) { // do stuff } As far as I know, you can't redefine null, so it's not going to break unexpectedly. And, because of the type-coercion of the != operator, this checks for both undefined and null... which is often exactly what you want (e.g. for optional function parameters). Yet this form does not seem widespread, and it even causes JSLint to yell at you for using the evil != operator. Why is this considered bad style?

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• Haskell: Constrain function on type Double to only work with Integers

  - by thurn

  Suppose I'm writing a function that takes a list of integers and returns only those integers in the list that are less than 5.2. I might do something like this: belowThreshold = filter (< 5.2) Easy enough, right? But now I want to constrain this function to only work with input lists of type [Int] for design reasons of my own. This seems like a reasonable request. Alas, no. A declaration that constraints the types as so: belowThreshold :: [Integer] -> [Integer] belowThreshold = filter (< 5.2) Causes a type error. So what's the story here? Why does doing filter (< 5.2) seem to convert my input list into Doubles? How can I make a version of this function that only accepts integer lists and only returns integer lists? Why does the type system hate me?

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