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  • Streaming Video In Scala InfoChannel Designer 5

    - by godleuf
    I am having the hardest time finding urls to use in Scala Designer 5 showing video streams. I am new at this program, but there is an option to run a video as a background. I have found a couple of samples to link to, but nothing great thus far. Anyone out there using this program and wanting to do the same? Thanks.

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  • Scala Hoogle equivalent?

    - by Alexey Romanov
    Hoogle allows you to search many standard Haskell libraries by either function name, or by approximate type signature. I find it very useful. Is there anything like Hoogle for Scala? Search in ScalaDoc 2 only finds types and packages by name.

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  • Simple Scala actor question

    - by 7zark7
    I'm sure this is a very simple question, but embarrassed to say I can't get my head around it: I have a list of values in Scala. I would like to use use actors to make some (external) calls with each value, in parallel. I would like to wait until all values have been processed, and then proceed. There's no shared values being modified. Could anyone advise? Thanks

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  • Best method to peek into a Scala Actor's Mailbox

    - by scaling_out
    Using Scala 2.8 RC1 or newer, what is the best (easiest and/or most direct) method to "peek" at the waiting messages in an actor's mailbox (from within the same actor's act() method) in order to examine what is in the queue, without having to react/receive the messages and/or disturb the current contents of the mailbox in any way. The purpose of this is so that an actor may determine if it is safe to process a request to exit by first determining if any of the remaining mailbox messages are ones that must be processed, instead of just dropped by stopping the actor immediately.

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  • Is scala's cake pattern possible with parametrized components?

    - by Nicolas
    Parametrized components work well with the cake pattern as long as you are only interested in a unique component for each typed component's, example: trait AComponent[T] { val a:A[T] class A[T](implicit mf:Manifest[T]) { println(mf) } } class App extends AComponent[Int] { val a = new A[Int]() } new App Now my application requires me to inject an A[Int] and an A[String], obviously scala's type system doesn't allow me to extends AComponent twice. What is the common practice in this situation ?

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  • Understanding Scope on Scala's For Loops (For Comprehension)

    - by T. Stone
    In Chapter 3 of Programming Scala, the author gives two examples of for loops / for comprehensions, but switches between using ()'s and {}'s. Why is this the case, as these inherently look like they're doing the same thing? Is there a reason breed <- dogBreeds is on the 2nd line in example #2? // #1 ()'s for (breed <- dogBreeds if breed.contains("Terrier"); if !breed.startsWith("Yorkshire") ) println(breed) // #2 {}'s for { breed <- dogBreeds upcasedBreed = breed.toUpperCase() } println(upcasedBreed)

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  • Scala unsatisfiable cyclic dependency in "table-layout" library (Toolkit class)

    - by Atol
    When I try to compile with sbt some code containing an instance of a Table from this library I get this error: java.lang.AssertionError: assertion failed: unsatisfiable cyclic dependency in 'class Toolkit' It seems to work with Java so I don't understand why it fails in Scala. Here is the toolkit class: http://code.google.com/p/table-layout/source/browse/branches/v1/tablelayout/src/com/esotericsoftware/tablelayout/Toolkit.java As long as I get this error I'm totally stopped in my project :(.

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  • Intersection() and Except() is too slow with large collections of custom objects

    - by Theo
    I am importing data from another database. My process is importing data from a remote DB into a List<DataModel> named remoteData and also importing data from the local DB into a List<DataModel> named localData. I am then using LINQ to create a list of records that are different so that I can update the local DB to match the data pulled from remote DB. Like this: var outdatedData = this.localData.Intersect(this.remoteData, new OutdatedDataComparer()).ToList(); I am then using LINQ to create a list of records that no longer exist in remoteData, but do exist in localData, so that I delete them from local database. Like this: var oldData = this.localData.Except(this.remoteData, new MatchingDataComparer()).ToList(); I am then using LINQ to do the opposite of the above to add the new data to the local database. Like this: var newData = this.remoteData.Except(this.localData, new MatchingDataComparer()).ToList(); Each collection imports about 70k records, and each of the 3 LINQ operation take between 5 - 10 minutes to complete. How can I make this faster? Here is the object the collections are using: internal class DataModel { public string Key1{ get; set; } public string Key2{ get; set; } public string Value1{ get; set; } public string Value2{ get; set; } public byte? Value3{ get; set; } } The comparer used to check for outdated records: class OutdatedDataComparer : IEqualityComparer<DataModel> { public bool Equals(DataModel x, DataModel y) { var e = string.Equals(x.Key1, y.Key1) && string.Equals(x.Key2, y.Key2) && ( !string.Equals(x.Value1, y.Value1) || !string.Equals(x.Value2, y.Value2) || x.Value3 != y.Value3 ); return e; } public int GetHashCode(DataModel obj) { return 0; } } The comparer used to find old and new records: internal class MatchingDataComparer : IEqualityComparer<DataModel> { public bool Equals(DataModel x, DataModel y) { return string.Equals(x.Key1, y.Key1) && string.Equals(x.Key2, y.Key2); } public int GetHashCode(DataModel obj) { return 0; } }

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  • Scala: Simple webservice

    - by Chris
    I'd like to create a simple webservice in scala similar to: http://www.artima.com/lejava/articles/threeminutes.html Is there an easy way to do this? EDIT: I found a tutorial for lift http://wiki.liftweb.net/index.php/HowTo_do_Web_Services. However this seems to be way too complicated for what I'm looking for.

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  • Would it make sense to have a separate Scala library in Android market?

    - by soc
    As far as I understand it is necessary for people using Scala for Android applications to bundle the Scala classes they used with their application. Considering this adds hundreds of kilobytes to each Scala app redundantly, would it be possible to build a Scala library which can be delivered over the market, so app writers can just depend on that library instead of bundling it themselves?

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  • Enhance Predfined Methods in Scala

    - by fratnk
    Base question: Why can I write in Scala just: println(10) Why don't I need to write: Console println(10) Followup question: How can I introduce a new method "foo" which is everywhere visible and usable like "println"?

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  • NullPointerException, Collections not storing data?

    - by Elliott
    Hi there, I posted this question earlier but not with the code in its entirety. The coe below also calls to other classes Background and Hydro which I have included at the bottom. I have a Nullpointerexception at the line indicate by asterisks. Which would suggest to me that the Collections are not storing data properly. Although when I check their size they seem correct. Thanks in advance. PS: If anyone would like to give me advice on how best to format my code to make it readable, it would be appreciated. Elliott package exam0607; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.net.URL; import java.util.Collection; import java.util.Scanner; import java.util.Vector; import exam0607.Hydro; import exam0607.Background;// this may not be necessary???? FIND OUT public class HydroAnalysis { public static void main(String[] args) { Collection hydroList = null; Collection backList = null; try{hydroList = readHydro("http://www.hep.ucl.ac.uk/undergrad/3459/exam_data/2006-07/final/hd_data.dat");} catch (IOException e){ e.getMessage();} try{backList = readBackground("http://www.hep.ucl.ac.uk/undergrad/3459/exam_data/2006-07/final/hd_bgd.dat"); //System.out.println(backList.size()); } catch (IOException e){ e.getMessage();} for(int i =0; i <=14; i++ ){ String nameroot = "HJK"; String middle = Integer.toString(i); String hydroName = nameroot + middle + "X"; System.out.println(hydroName); ALGO_1(hydroName, backList, hydroList); } } public static Collection readHydro(String url) throws IOException { URL u = new URL(url); InputStream is = u.openStream(); InputStreamReader isr = new InputStreamReader(is); BufferedReader b = new BufferedReader(isr); String line =""; Collection data = new Vector(); while((line = b.readLine())!= null){ Scanner s = new Scanner(line); String name = s.next(); System.out.println(name); double starttime = Double.parseDouble(s.next()); System.out.println(+starttime); double increment = Double.parseDouble(s.next()); System.out.println(+increment); double p = 0; double nterms = 0; while(s.hasNextDouble()){ p = Double.parseDouble(s.next()); System.out.println(+p); nterms++; System.out.println(+nterms); } Hydro SAMP = new Hydro(name, starttime, increment, p); data.add(SAMP); } return data; } public static Collection readBackground(String url) throws IOException { URL u = new URL(url); InputStream is = u.openStream(); InputStreamReader isr = new InputStreamReader(is); BufferedReader b = new BufferedReader(isr); String line =""; Vector data = new Vector(); while((line = b.readLine())!= null){ Scanner s = new Scanner(line); String name = s.next(); //System.out.println(name); double starttime = Double.parseDouble(s.next()); //System.out.println(starttime); double increment = Double.parseDouble(s.next()); //System.out.println(increment); double sum = 0; double p = 0; double nterms = 0; while((s.hasNextDouble())){ p = Double.parseDouble(s.next()); //System.out.println(p); nterms++; sum += p; } double pbmean = sum/nterms; Background SAMP = new Background(name, starttime, increment, pbmean); //System.out.println(SAMP); data.add(SAMP); } return data; } public static void ALGO_1(String hydroName, Collection backgs, Collection hydros){ //double aMin = Double.POSITIVE_INFINITY; //double sum = 0; double intensity = 0; double numberPN_SIG = 0; double POSITIVE_PN_SIG =0; //int numberOfRays = 0; for(Hydro hd: hydros){ System.out.println(hd.H_NAME); for(Background back : backgs){ System.out.println(back.H_NAME); if(back.H_NAME.equals(hydroName)){//ERROR HERE double PN_SIG = Math.max(0.0, hd.PN - back.PBMEAN); numberPN_SIG ++; if(PN_SIG 0){ intensity += PN_SIG; POSITIVE_PN_SIG ++; } } } double positive_fraction = POSITIVE_PN_SIG/numberPN_SIG; if(positive_fraction < 0.5){ System.out.println( hydroName + "is faulty" ); } else{System.out.println(hydroName + "is not faulty");} System.out.println(hydroName + "has instensity" + intensity); } } } THE BACKGROUND CLASS package exam0607; public class Background { String H_NAME; double T_START; double DT; double PBMEAN; public Background(String name, double starttime, double increment, double pbmean) { name = H_NAME; starttime = T_START; increment = DT; pbmean = PBMEAN; }} AND THE HYDRO CLASS public class Hydro { String H_NAME; double T_START; double DT; double PN; public double n; public Hydro(String name, double starttime, double increment, double p) { name = H_NAME; starttime = T_START; increment = DT; p = PN; } }

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  • What's the difference between these two calls to a function taking a collection of structural types?

    - by James Moore
    Why does the call to fn(Iterator("foo") compile, but the call to fn(fooIterator) fail with an error "type mismatch; found : Iterator[java.lang.String] required: scala.Iterator[com.banshee.Qx.HasLength]" object Qx { type HasLength = {def length: Int} def fn(xs: Iterator[HasLength]) = 3 var tn = fn(Iterator("foo")) var fooIterator = Iterator("foo") var tnFails = fn(fooIterator) //doesn't compile } Aren't they the same thing?

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  • What is a "context bound"?

    - by Jesper
    One of the new features of Scala 2.8 are context bounds. What is a context bound and where is it useful? Of course I searched first (and found for example this) but I couldn't find any really clear and detailed information.

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  • Don't understand the typing of Scala's delimited continuations (A @cps[B,C])

    - by jkff
    I'm struggling to understand what precisely does it mean when a value has type A @cps[B,C] and what types of this form should I assign to my values when using the delimited continuations facility. I've looked at some sources: http://lamp.epfl.ch/~rompf/continuations-icfp09.pdf http://www.scala-lang.org/node/2096 http://dcsobral.blogspot.com/2009/07/delimited-continuations-explained-in.html http://blog.richdougherty.com/2009/02/delimited-continuations-in-scala_24.html but they didn't give me much intuition into this. In the last link, the author tries to give an explicit explanation, but it is not clear enough anyway. The A here represents the output of the computation, which is also the input to its continuation. The B represents the return type of that continuation, and the C represents its "final" return type—because shift can do further processing to the returned value and change its type. I don't understand the difference between "output of the computation", "return type of the continuation" and "final return type of the continuation". They sound like synonyms.

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  • Which Java-specific annoyance fixed in Scala reduces surprises like the ones discussed in Java Puzzl

    - by soc
    Example: In Java this code falls through and prints "Mhhh..." Integer i = new Integer(1); Integer j = new Integer(1); if (i == j) { System.out.println("Equal"); } else if (i < j) { System.out.println("Smaller"); } else if (i > j) { System.out.println("Bigger"); } else {System.out.println("Mhhh...");} In Scala the equivalent code does not even compile: val a = new Integer(1) val b = new Integer(1) println { if(a == b) "Equal" else if(a < b) "Smaller" else if (a > b) "Bigger" else "Mhhh..."}

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  • Scala: working around the "illegal cyclic reference"

    - by Paul Milovanov
    Hi all, I'm trying to implement a HashMap-based tree that'd support O(1) subtree lookup for a given root key. To that goal, I'm trying to do the following: scala> type Q = HashMap[Char, Q] <console>:6: error: illegal cyclic reference involving type Q type Q = HashMap[Char, Q] ^ So the question is, is there a way for me to do something of the sort without resorting to the ugly HashMap[Char, Any] with subsequent casting of values to HashMap[Char, Any]? Now, I also see that I can use something like the following to avoid the cyclic-reference error, and it might even be cleaner -- but it'd be nice to find out how to correctly do it the first way, just for the educational value. import collections.mutable.HashMap class LTree { val children = new HashMap[Char, LTree] } Thanks a bunch.

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  • ZeroC Ice "checked casts" in Scala

    - by Alexey Romanov
    ZeroC Ice for Java translates every Slice interface Simple into (among other things) a proxy interface SimplePrx and a proxy SimplePrxHelper. If I have an ObjectPrx (the base interface for all proxies), I can check whether it actually has interface Simple by using a static method on SimplePrxHelper: val obj : Ice.ObjectPrx = ...; // Get a proxy from somewhere... val simple : SimplePrx = SimplePrxHelper.checkedCast(obj); if (simple != null) // Object supports the Simple interface... else // Object is not of type Simple... I wanted to write a method castTo so that I could replace the second line with val simple = castTo[SimplePrx](obj) or val simple = castTo[SimplePrxHelper](obj) So far as I can see, Scala's type system is not expressive enough to allow me to define castTo. Is this correct?

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  • Error after installing scala plugin of netbeans

    - by ghedas
    I installed the scala plugin on my netbeans and followed the instruction of this page: http://wiki.netbeans.org/Scala68v1#Scala_Plugins_for_NetBeans_6.8_v1.x_.28RC2.29 but after it completed correctly step by step, when I make an empty project (Hello world!), the project has an error! The empty project is here: package scalaapplication1 object Main { /** * @param args the command line arguments */ def main(args: Array[String]): Unit = { println("Hello, world!") } } and the console error report is: ...\NetBeansProjects\ScalaApplication2\nbproject\build-impl.xml:403: The following error occurred while executing this line: ...\NetBeansProjects\ScalaApplication2\nbproject\build-impl.xml:236: scalac doesn't support the "fork" attribute Is there any suggestion about it?!

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  • Multiple return points in scala closure/anonymous function

    - by Debilski
    As far as I understand it, there is no way in Scala to have multiple return points in an anonymous function, i.e. someList.map((i) => { if (i%2 == 0) return i // the early return allows me to avoid the else clause doMoreStuffAndReturnSomething(i) }) raises an error: return outside method definition. (And if it weren’t to raise that, the code would not work as I’d like it to work.) One workaround I could thing of would be the following someList.map({ def f(i: Int):Int = { if (i%2 == 0) return i doMoreStuffAndReturnSomething(i) } f }) however, I’d like to know if there is another ‘accepted’ way of doing this. Maybe a possibility to go without a name for the inner function? (A use case would be to emulate some valued continue construct inside the loop.)

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