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• How to compose a Matcher[Iterable[A]] from a Matcher[A] with specs testing framework

  - by Garrett Rowe

  If I have a Matcher[A] how do create a Matcher[Iterable[A]] that is satisfied only if each element of the Iterable satisfies the original Matcher. class ExampleSpec extends Specification { def allSatisfy[A](m: => Matcher[A]): Matcher[Iterable[A]] = error("TODO") def notAllSatisfy[A](m: => Matcher[A]): Matcher[Iterable[A]] =…

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• Concatenating databases with Squeryl

  - by Pengin

  I'm trying to use Squeryl to take the contents of a table from one database, and append it to the equivalent table in another database. The primary key will have to be reassigned in the process, but I'm getting the error NULL not allowed for column "SIMID". Why is this? object Concatenator { def main(args: Array[String]) { …

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• A rapid way to type funny characters from Scalaz ?

  - by Green Hyena

  Is there any easy and fast way to type the funny characters (like ??, ??, ??, ?? etc) from Scalaz? (I am using Ubuntu 9.04)

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• Parsing a dynamic value with Lift-JSON

  - by Surya Suravarapu

  Let me explain this question with an example. If I have a JSON like the following: {"person1":{"name": "Name One", "address": {"street": "Some Street","city": "Some City"}}, "person2":{"name": "Name Two", "address": {"street": "Some Other Street","city": "Some Other City"}}} [There is no restriction on the number…

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• Zip elements with odd and even indices in a list

  - by Alexander Temerev

  I want to zip even and odd elements in a list to make a list of pairs, like that: ["A", "B", "C", "D", "E", "F"] -> [("A", "B"), ("C", "D"), ("E", "F")] What is the most concise expression to do this in elegant in functional way?

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• How do I rewrite a for loop with a shared dependency using actors

  - by Thomas Rynne

  We have some code which needs to run faster. Its already profiled so we would like to make use of multiple threads. Usually I would setup an in memory queue, and have a number of threads taking jobs of the queue and calculating the results. For the shared data I would use a ConcurrentHashMap or similar. I don't really want to…

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• Parsing HTTP - Bytes.length != String.length

  - by hotzen

  Hello, I consume HTTP via nio.SocketChannel, so I get chunks of data as Array[Byte]. I want to put these chunks into a parser and continue parsing after each chunk has been put. HTTP itself seems to use an ISO8859-Charset but the Payload/Body itself may be arbitrarily encoded: If the HTTP Content-Length specifies X bytes,…

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• how to define a structural type that refers to itself?

  - by IttayD

  I want to create a method sum that I can call on different types, specifically sum(1,2). def sum[A](a1: A, a2: A) = a1 + a2 This fails because the compiler can't tell if A has a method '+' I tried to define a structural type: type Addable = {def +(a: Addable)} This fails because of an illegal cyclic reference How can…

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• An Actor "queue" ?

  - by synic

  In Java, to write a library that makes requests to a server, I usually implement some sort of dispatcher (not unlike the one found here in the Twitter4J library: http://github.com/yusuke/twitter4j/blob/master/twitter4j-core/src/main/java/twitter4j/internal/async/DispatcherImpl.java) to limit the number of connections, to…

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• Straight Java/Groovy versus ETL tool (Talend/etc) - what libraries would you use?

  - by Alex R

  Assume you have a small project which on the surface looks like a good match for an ETL tool like Talend. But assume further, that you have never used Talend and furthermore, you do not trust "visual programming" tools in general and would rather code everything the old fashioned way (text on a nice IDE!) with the help…

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• Higher-kinded Types with C++

  - by Venkat Shiva

  This question is for the people who know both Haskell (or any other functional language that supports Higher-kinded Types) and C++... Is it possible to model higher kinded types using C++ templates? If yes, then how?

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• defining a simple implicit Arbitary

  - by FredOverflow

  I have a type Foo with a constructor that takes an Int. How do I define an implicit Arbitrary for Foo to be used with scalacheck? implicit def arbFoo: Arbitrary[Foo] = ??? I came up with the following solution, but it's a bit too "manual" and low-level for my taste: val fooGen = for (i <- Gen.choose(Int.MinValue,…

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• Initialising vals which might throw an exception

  - by Paul Butcher

  I need to initialise a set of vals, where the code to initialise them might throw an exception. I'd love to write: try { val x = ... generate x value ... val y = ... generate y value ... } catch { ... exception handling ... } ... use x and y ... But this (obviously) doesn't work because x and y aren't in scope…

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• How to get list of traits that were mixed in the specified class?

  - by Jeriho

  And more specific example: abstract trait A trait B extends A trait C extends A How to check what traits that extend trait A (it can be from 0 to many) were mixed in specified class?

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• Named parameters lead to inferior readability?

  - by Thomas Jung

  With named parameters like def f(x : Int = 1, y : Int = 2) = x * y your parameter names become part of the interface f(x=3) Now if you want to change the parameter names locally, you are forced to perserve the public name of the parameter: def f(x : Int = 1, y : Int = 2) = { val (a,b) = (x,y) a * b } …

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• Modify iterator

  - by isola009

  I have a iterator (ite) created from a set (a): var a = Set(1,2,3,4,5) var ite = a.iterator If I remove 2 element of my set: a -= 2 Now, if I move iterator for all elements, I get all elements (2 element included). It's ok, but... How I can tell to iteratator to delete 2 element?

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• How to use SBT (Simple Build Tool) with Google App Engine?

  - by Rafal Sobota

  Has anybody tried to setup SBT to work with Google App Engine? I dream about using development server auto-reloading after source changes.

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• Liftweb Menu customization

  - by DataSurfer

  I want to create a menu that looks like: HOME | FOO | BAR | ABOUT | CONTACT How might I go about doing this? Here is what I have tried: <lift:Menu.builder ul:class="menu" li_item:class="current" /> and ul.menu li { display: inline; list-style-type: none; text-transform: uppercase; …

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• S.redirectTo leads always to a blank screen

  - by Jaime Ocampo

  I am now playing a little bit with lift (2.8.0), and all the features in LiftRules work as intended. But I haven't been able to use S.redirectTo at all. I always ends with a blank screen, no matter what. No error messages at all! As an example, I have the following form: ... <lift:logIn.logInForm…

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• Example of contravariance

  - by Misha

  I am thinking of the following example to illustrate why contravariance is useful. Let's consider a GUI framework with Widgets, Events, and Event Listeners. abstract class Event; class KeyEvent extends Event class MouseEvent extends Event trait EventListener[-Event] { def listen(e:Event) } Let…

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• What is a good architecture for a Lift-JPA application?

  - by egervari

  I was wondering what is the best practice for a JPA model in Lift? I noticed that in the jpa demo application, there is just a Model object that is like a super object that does everything. I don't think this can be the most scalable approach, no? Is it is wise to still do the DAO pattern in…

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• Creating classes that can be instantiated with single or multiple elements as constructor's argument

  - by Jeriho

  I want to have class that can be instantiated with list, array, seq, set, stack, queue etc. In my opinion class A class B(elems:A*) should handle such stuff. This is my solution: class A class B(elems:Iterable[A]){ def this(elem:A) = this(Seq(elem)) } Can you suggest any…

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• How does Play recognize a particular websocket message?

  - by noncom

  I am looking at the websocket-chat example. It unveils much, but I still cannot get something. I understand how messages are received, processed and sent on the web page side. However, Play captures websocket messages by means of the receive method of an Akka actor. In the…

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• Is it possible to use the ScalaTest BDD syntax in a JUnit environment?

  - by ebruchez

  I would like to describe tests in BDD style e.g. with FlatSpec but keep JUnit as a test runner. The ScalaTest Quick Start does not seem to show any example of this: http://www.scalatest.org/getting_started_with_junit_4 I first tried naively to write tests within @Test…

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• Immutability and shared references - how to reconcile?

  - by davetron5000

  Consider this simplified application domain: Criminal Investigative database Person is anyone involved in an investigation Report is a bit of info that is part of an investigation A Report references a primary Person (the subject of an investigation) A Report has…

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