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  • Dependency between operations in scala actors

    - by paradigmatic
    I am trying to parallelise a code using scala actors. That is my first real code with actors, but I have some experience with Java Mulithreading and MPI in C. However I am completely lost. The workflow I want to realise is a circular pipeline and can be described as the following: Each worker actor has a reference to another one, thus forming a circle There is a coordinator actor which can trigger a computation by sending a StartWork() message When a worker receives a StartWork() message, it process some stuff locally and sends DoWork(...) message to its neighbour in the circle. The neighbours do some other stuff and sends in turn a DoWork(...) message to its own neighbour. This continues until the initial worker receives a DoWork() message. The coordinator can send a GetResult() message to the initial worker and wait for a reply. The point is that the coordinator should only receive a result when data is ready. How can a worker wait that the job returned to it before answering the GetResult() message ? To speed up computation, any worker can receive a StartWork() at any time. Here is my first try pseudo-implementation of the worker: class Worker( neighbor: Worker, numWorkers: Int ) { var ready = Foo() def act() { case StartWork() => { val someData = doStuff() neighbor ! DoWork( someData, numWorkers-1 ) } case DoWork( resultData, remaining ) => if( remaining == 0 ) { ready = resultData } else { val someOtherData = doOtherStuff( resultData ) neighbor ! DoWork( someOtherData, remaining-1 ) } case GetResult() => reply( ready ) } } On the coordinator side: worker ! StartWork() val result = worker !? GetResult() // should wait

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  • initialising a 2-dim Array in Scala

    - by Stefan W.
    (Scala 2.7.7:) I don't get used to 2d-Arrays. Arrays are mutable, but how do I specify a 2d-Array which is - let's say of size 3x4. The dimension (2D) is fixed, but the size per dimension shall be initializable. I tried this: class Field (val rows: Int, val cols: Int, sc: java.util.Scanner) { var field = new Array [Char](rows)(cols) for (r <- (1 to rows)) { val line = sc.nextLine () val spl = line.split (" ") field (r) = spl.map (_.charAt (0)) } def put (val rows: Int, val cols: Int, c: Char) = todo () } I get this error: :11: error: value update is not a member of Char field (r) = spl.map (_.charAt (0)) If it would be Java, it would be much more code, but I would know how to do it, so I show what I mean: public class Field { private char[][] field; public Field (int rows, int cols, java.util.Scanner sc) { field = new char [rows][cols]; for (int r = 0; r < rows; ++r) { String line = sc.nextLine (); String[] spl = line.split (" "); for (int c = 0; c < cols; ++c) field [r][c] = spl[c].charAt (0); } } public static void main (String args[]) { new Field (3, 4, new java.util.Scanner ("fraese.fld")); } } and fraese.fld would look, for example, like that: M M M M . M I get some steps wide with val field = new Array Array [Char] but how would I then implement 'put'? Or is there a better way to implement the 2D-Array. Yes, I could use a one-dim-Array, and work with put (y, x, c) = field (y * width + x) = c but I would prefer a notation which looks more 2d-ish.

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  • How to store child objects on GAE using JDO from Scala

    - by Gero
    Hi, I'm have a parent-child relation between 2 classes, but the child objects are never stored. I do get an warning: "org.datanucleus.store.appengine.MetaDataValidator checkForIllegalChildField: Unable to validate relation net.vermaas.kivanotify.model.UserCriteria.internalCriteria" but it is unclear to me why this occurs. Already tried several alternatives without luck. The parent class is "UserCriteria" which has a List of "Criteria" as children. The classes are defined as follows (Scala): class UserCriteria(tu: String, crit: Map[String, String]) extends LogHelper { @PrimaryKey @Persistent{val valueStrategy = IdGeneratorStrategy.IDENTITY} var id = KeyFactory.createKey("UserCriteria", System.nanoTime) @Persistent var twitterUser = tu @Persistent var internalCriteria: java.util.List[Criteria] = flatten(crit) def flatten(crits: Map[String, String]) : java.util.List[Criteria] = { val list = new java.util.ArrayList[Criteria] for (key <- crits.keySet) { list.add(new Criteria(this, key, crits(key))) } list } def criteria: Map[String, String] = { val crits = mutable.Map.empty[String, String] for (i <- 0 to internalCriteria.size-1) { crits(internalCriteria.get(i).name) = internalCriteria.get(i).value } Map.empty ++ crits } // Stripped the equals, canEquals, hashCode, toString code to keep the code snippet short... } @PersistenceCapable @EmbeddedOnly class Criteria(uc: UserCriteria, nm: String, vl: String) { @Persistent var userCriteria = uc @Persistent var name = nm @Persistent var value = vl override def toString = { "Criteria name: " + name + " value: " + value } } Any ideas why the childs are not stored? Or why I get the error message? Thanks, Gero

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  • Trait, FunctionN, or trait-inheriting-FunctionN in Scala?

    - by Willis Blackburn
    I have a trait in Scala that has a single method. Call it Computable and the single method is compute(input: Int): Int. I can't figure out whether I should Leave it as a standalone trait with a single method. Inherit from (Int = Int) and rename "compute" to "apply." Just get rid of Computable and use (Int = Int). A factor in favor of it being a trait is that I could usefully add some additional methods. But of course if they were all implemented in terms of the compute method then I could just break them out into a separate object. A factor in favor of just using the function type is simplicity and the fact that the syntax for an anonymous function is more concise than that for an anonymous Computable instance. But then I've no way to distinguish objects that are actually Computable instances from other functions that map Int to Int but aren't meant to be used in the same context as Computable. How do other people approach this type of problem? No right or wrong answers here; I'm just looking for advice.

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  • What is the worst real-world macros/pre-processor abuse you've ever come across?

    - by Trevor Boyd Smith
    What is the worst real-world macros/pre-processor abuse you've ever come across (please no contrived IOCCC answers *haha*)? Please add a short snippet or story if it is really entertaining. The goal is to teach something instead of always telling people "never use macros". p.s.: I've used macros before... but usually I get rid of them eventually when I have a "real" solution (even if the real solution is inlined so it becomes similar to a macro). Bonus: Give an example where the macro was really was better than a not-macro solution. Related question: When are C++ macros beneficial?

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  • Doesn't (didn't) Scala have automatically generated setters?

    - by Malvolio
    Google and my failing memory are both giving me hints that it does, but every attempt is coming up dry. class Y { var y = 0 } var m = new Y() m.y_(3) error: value y_ is not a member of Y Please tell me I am doing something wrong. (Also: please tell me what it is I am doing wrong.) EDIT The thing I am not doing wrong, or at least not the only thing I am doing wrong, is the way I am invoking the setter. The following things also fail, all with the same error message: m.y_ // should be a function valued expression m.y_ = (3) // suggested by Google and by Mchl f(m.y_) // where f takes Int => Unit as an argument f(m.y) // complains that I am passing in Int not a function I am doing this all through SimplyScala, because I'm too lazy and impatient to set up Scala on my tiny home machine. Hope it isn't that... And the winner is ... Fabian, who pointed out that I can't have a space between the _ and the =. I thought out why this should be and then it occurred to me: The name of the setter for y is not y_, it is y_= ! Observe: class Y { var y = 0 } var m = new Y() m.y_=(3) m.y res1: Int = 3 m.y_= error: missing arguments for method y_= in class Y; follow this method with `_` if you want to treat it as a partially applied function m.y_= ^ m.y_=_ res2: (Int) => Unit = def four(f : Int => Unit) = f(4) four(m.y_=) m.y res3: Int = 4 Another successful day on StackExchange.

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  • Implicit conversion between Scala collection types

    - by ebruchez
    I would like to implicitly convert between the Scala XML Elem object and another representation of an XML element, in my case dom4j Element. I wrote the following implicit conversions: implicit def elemToElement(e: Elem): Element = ... do conversion here ... implicit def elementToElem(e: Element): Elem = ... do conversion here ... So far so good, this works. Now I also need collections of said elements to convert both ways. First, do I absolutely need to write additional conversion methods? Things didn't seem to work if I didn't. I tried to write the following: implicit def elemTToElementT(t: Traversable[Elem]) = t map (elemToElement(_)) implicit def elementTToElemT(t: Traversable[Element]) = t map (elementToElem(_)) This doesn't look too ideal because if the conversion method takes a Traversable, then it also returns a Traversable. If I pass a List, I also get a Traversable out. So I assume the conversion should be parametrized somehow. So what's the standard way of writing these conversions in order to be as generic as possible?

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  • Scala always returning true....WHY?

    - by jhamm
    I am trying to learn Scala and am a newbie. I know that this is not optimal functional code and welcome any advice that anyone can give me, but I want to understand why I keep getting true for this function. def balance(chars: List[Char]): Boolean = { val newList = chars.filter(x => x.equals('(') || x.equals(')')); return countParams(newList, 0) } def countParams(xs: List[Char], y: Int): Boolean = { println(y + " right Here") if (y < 0) { println(y + " Here") return false } else { println(y + " Greater than 0") if (xs.size > 0) { println(xs.size + " this is the size") xs match { case xs if (xs.head.equals('(')) => countParams(xs.tail, y + 1) case xs if (xs.head.equals(')')) => countParams(xs.tail, y - 1) case xs => 0 } } } return true; } balance("()())))".toList) I know that I am hitting the false branch of my if statement, but it still returns true at the end of my function. Please help me understand. Thanks.

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  • best web database solution for scala for a high traffic site?

    - by egervari
    I am in charge of a rebuilding a website that gets about 250,000 visitors a day. We'd like to use Scala, but it does not work very well with Spring (in some minor cases) and Hibernate (there is a major and very annoying mismatch here if you want to use scala collections, which we do). The application itself is going to have about 40-50 tables. Other than Hibernate, is there an ORM that works awesome with Scala and is as performant and reliable as Hibernate? Does it also have the same capabilities, or are we going to run into leaky-abstractions if we don't use Hibernate? It would be a big risk for us to go with a framework that is newer and doesn't seem to have a lot of industry backing... and at the same time, Hibernate is a real pain to program against when using Scala. 1) The Java Collection <- Scala Collection is absolutely painful. There is a lot more boilerplate and crap to write. 2) The IDE doesn't import JavaConversions and java interfaces automatically... so we this needs to be done manually. Optimizing Imports in IDEA is going to destroy all the manual work. 3) There is also a performance cost to converting back and forth all the time in your domain objects and your dao classes. 4) Not to mention there needs to be a lot of casting, which produces code ugly as sin. I actually would love to write my own orm that is 100% tailored to scala, but obviously this is really outside of the scope of our project for now. So what is the best approach?

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  • How to implement collection with covariance when delegating to another collection for storage?

    - by memelet
    I'm trying to implement a type of SortedMap with extended semantics. I'm trying to delegate to SortedMap as the storage but can't get around the variance constraints: class IntervalMap[A, +B](implicit val ordering: Ordering[A]) //extends ... { var underlying = SortedMap.empty[A, List[B]] } Here is the error I get. I understand why I get the error (I understand variance). What I don't get is how to implement this type of delegation. And yes, the covariance on B is required. error: covariant type B occurs in contravariant position in type scala.collection.immutable.SortedMap[A,List[B]] of parameter of setter underlying_=

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  • [Scala] Using overloaded, typed methods on a collection

    - by stephanos
    I'm quite new to Scala and struggling with the following: I have database objects (type of BaseDoc) and value objects (type of BaseVO). Now there are multiple convert methods (all called 'convert') that take an instance of an object and convert it to the other type accordingly. For example: def convert(doc: ClickDoc): ClickVO = doc match { case null => null case _ => val result = new ClickVO result.x = doc.x result.y = doc.y result } Now I sometimes need to convert a list of objects. How would I do this - I tried: def convert[D <: MyBaseDoc, V <: BaseVO](docs: List[D]):List[V] = docs match { case List() => List() case xs => xs.map(doc => convert(doc)) } Which results in 'overloaded method value convert with alternatives ...'. I tried to add manifest information to it, but couldn't make it work. I couldn't even create one method for each because it'd say that they have the same parameter type after type erasure (List). Ideas welcome!

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  • Macro access to members of object where macro is defined

    - by Marc Grue
    Say I have a trait Foo that I instantiate with an initial value val foo = new Foo(6) // class Foo(i: Int) and I later call a second method that in turn calls myMacro foo.secondMethod(7) // def secondMethod(j: Int) = macro myMacro then, how can myMacro find out what my initial value of i (6) is? I didn't succeed with normal compilation reflection using c.prefix, c.eval(...) etc but instead found a 2-project solution: Project B: object CompilationB { def resultB(x: Int, y: Int) = macro resultB_impl def resultB_impl(c: Context)(x: c.Expr[Int], y: c.Expr[Int]) = c.universe.reify(x.splice * y.splice) } Project A (depends on project B): trait Foo { val i: Int // Pass through `i` to compilation B: def apply(y: Int) = CompilationB.resultB(i, y) } object CompilationA { def makeFoo(x: Int): Foo = macro makeFoo_impl def makeFoo_impl(c: Context)(x: c.Expr[Int]): c.Expr[Foo] = c.universe.reify(new Foo {val i = x.splice}) } We can create a Foo and set the i value either with normal instantiation or with a macro like makeFoo. The second approach allows us to customize a Foo at compile time in the first compilation and then in the second compilation further customize its response to input (i in this case)! In some way we get "meta-meta" capabilities (or "pataphysic"-capabilities ;-) Normally we would need to have foo in scope to introspect i (with for instance c.eval(...)). But by saving the i value inside the Foo object we can access it anytime and we could instantiate Foo anywhere: object Test extends App { import CompilationA._ // Normal instantiation val foo1 = new Foo {val i = 7} val r1 = foo1(6) // Macro instantiation val foo2 = makeFoo(7) val r2 = foo2(6) // "Curried" invocation val r3 = makeFoo(6)(7) println(s"Result 1 2 3: $r1 $r2 $r3") assert((r1, r2, r3) ==(42, 42, 42)) } My question Can I find i inside my example macros without this double compilation hackery?

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  • Using the RSSBus Salesforce Excel Add-In From Excel Macros (VBA)

    - by dataintegration
    The RSSBus Salesforce Excel Add-In makes it easy to retrieve and update data from Salesforce from within Microsoft Excel. In addition to the built-in wizards that make data manipulation possible without code, the full functionality of the RSSBus Excel Add-Ins is available programmatically with Excel Macros (VBA) and Excel Functions. This article shows how to write an Excel macro that can be used to perform bulk inserts into Salesforce. Although this article uses the Salesforce Excel Add-In as an example, the same process can be applied to any of the Excel Add-Ins available on our website. Step 1: Download and install the RSSBus Excel Add-In available on our website. Step 2: Open Excel and create place holder cells for the connection details that are needed from the macro. In this article, a spreadsheet will be created for batch inserts, and these cells will store the connection details, and will be used to report the job Id, the batch Id, and the batch status. Step 3: Switch to the Developer tab in Excel. Add a new button on the spreadsheet, and create a new macro associated with it. This macro will contain the code needed to insert a batch of rows into Salesforce. Step 4: Add a reference to the Excel Add-In by selecting Tools --> References --> RSSBus Excel Add-In. The macro functions of the Excel Add-In will be available once the reference has been added. The following code shows how to call a Stored Procedure. In this example, a job is created to insert Leads by calling the CreateJob stored procedure. CreateJob returns a jobId that can be used to upload a large number of Leads in one transaction. Note the use of cells B1, B2, B3, and B4 that were created in Step 2 to read the connection settings from the Excel SpreadSheet and to write out the status of the procedure. methodName = "CreateJob" module.SetProviderName ("Salesforce") nameArray = Array("ObjectName", "Action", "ConcurrencyMode") valueArray = Array("Lead", "insert", "Serial") user = Range("B1").value pass = Range("B2").value atoken = Range("B3").value If (Not user = "" And Not pass = "" And Not atoken = "") Then module.SetConnectionString ("User=" + user + ";Password=" + pass + ";Access Token=" + atoken + ";") If module.CallSP(methodName, nameArray, valueArray) Then Dim ColumnCount As Integer ColumnCount = module.GetColumnCount Dim idIndex As Integer For Count = 0 To ColumnCount - 1 Dim colName As String colName = module.GetColumnName(Count) If module.GetColumnName(Count) = "id" Then idIndex = Count End If Next While (Not module.EOF) Range("B4").value = module.GetValue(idIndex) module.MoveNext Wend Else MsgBox "The CreateJob query failed." End If Exit Sub Else MsgBox "Please specify the connection details." Exit Sub End If Error: MsgBox "ERROR: " & Err.Description Step 5: Add the code to your macro. If you use the code above, you can check the results at Salesforce.com. They can be seen at Administration Setup -> Monitoring -> Bulk Data Load Jobs. Download the attached sample file for a more complete demo. Distributing an Excel File With Macros An Excel file with macros is saved using the .xlms extension. The code for the macro remains in the Excel file, and you can distribute your Excel file to any machine where the RSSBus Salesforce Excel Add-In is already installed. Macro Sample File Please download the fully functional sample excel file that includes the code referenced here. You will also need the RSSBus Excel Add-In to make the connection. You can download a free trial here. Note: You may get an error message stating: "Can't find project or library." in Excel 2007, since this example is made using Excel 2010. To resolve this, navigate to Tools -> References and uncheck the "MISSING: RSSBus Excel Add-In", then scroll down and check the "RSSBus Excel Add-In" listed below it.

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  • Visual Studio 2012 first impressions...no Macros!

    - by bconlon
    Yesterday I installed Microsoft Visual Studio 2012 for the first time (all 8.5GB) and after 20 years of (mostly) happy times using VS they have removed Macros, one of the most handy features.The first thing I wanted to do when I upgraded my VS2010 project was to add a #elseif block to each file. This would usually be simple case of find in files of the previous #elseif and then Ctrl+Shift+R to record a macro which would be: F8 (to select the next file from find list), F3 (to find the correct position in file), Ctrl+V to paste the new code. Then all I would need to do is keep Ctrl+Shift+P (Play Macro) pressed until all the files were processed.But alas Ctrl+Shift+R does nothing! I won’t say that I use Macros every day but it was a very useful feature.To continue my moaning a little more, I also don't like the bland interface. This has been well documented by others, but now I have used it myself, I find it difficult to tell one grey area of screen from another and the lack of colour makes the icons unclear.I also don't see why the menus now need to SHOUT in capital letters?On the plus side, they have now added the ability to see WPF properties in the debugger...a bit of an oversight in Visual Studio 2010. Oh, but you still can't edit and continue on files that contain templated code.Whilst Visual Studio 2012 is not a complete disaster like Windows 8 (why develop a desk top OS to be the same as a Smart device OS), it does not float my boat.Rant over.#

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  • Why no more macro languages?

    - by Muhammad Alkarouri
    In this answer to a previous question of mine about scripting languages suitability as shells, DigitalRoss identifies the difference between the macro languages and the "parsed typed" languages in terms of string treatment as the main reason that scripting languages are not suitable for shell purposes. Macro languages include nroff and m4 for example. What are the design decisions (or compromises) needed to create a macro programming language? And why are most of the mainstream languages parsed rather than macro? This very similar question (and the accepted answer) covers fairly well why the parsed typed languages, take C for example, suffer from the use of macros. I believe my question here covers different grounds: Macro languages or those working on a textual level are not wholly failures. Arguably, they include bash, Tcl and other shell languages. And they work in a specific niche such as shells as explained in my links above. Even m4 had a fairly long time of success, and some of the web template languages can be regarded as macro languages. It is quite possible that macros and parsed typing do not go well together and that is why macros "break" common languages. In the answer to the linked question, a macro like #define TWO 1+1 would have been covered by the common rules of the language rather than conflicting with those of the host language. And issues like "macros are not typed" and "code doesn't compile" are not relevant in the context of a language designed as untyped and interpreted with little concern for efficiency. The question about the design decisions needed to create a macro language pertain to a hobby project which I am currently working on on designing a new shell. Taking the previous question in context would clarify the difference between adding macros to a parsed language and my objective. I hope the clarification shows that the question linked doesn't cover this question, which is two parts: If I want to create a macro language (for a shell or a web template, for example), what limitations and compromises (and guidelines, if exist) need to be done? (Probably answerable by a link or reference) Why have no macro languages succeed in becoming mainstream except in particular niches? What makes typed languages successful in large programming, while "stringly-typed" languages succeed in shells and one-liner like environments?

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  • PlayFramework with Scala and Morphia

    - by AKRamkumar
    I keep getting this exception: Oops: CannotCompileException An unexpected error occured caused by exception CannotCompileException: [source error] ds() not found in models.dc What is wrong with my code? Here is models.ds package models import com.google.code.morphia.annotations._ @Embedded class ds{ @Indexed var xs : Double=0 @Indexed var xc : Double=0 @Indexed var ys : Double=0 @Indexed var yc : Double=0 @Indexed var zs : Double=0 @Indexed var zc : Double=0 } Here is models.dc package models import com.google.code.morphia.annotations.{Embedded, Entity, Indexed} @Entity class dc{ @Indexed var name : String = null @Embedded var summary : ds = new ds() }

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  • Slow Scala assert

    - by Dave
    We've been profiling our code recently and we've come across a few annoying hotspots. They're in the form assert(a == b, a + " is not equal to " + b) Because some of these asserts can be in code called a huge amount of times the string concat starts to add up. assert is defined as: def assert(assumption : Boolean, message : Any) = .... why isn't it defined as: def assert(assumption : Boolean, message : => Any) = .... That way it would evaluate lazily. Given that it's not defined that way is there an inline way of calling assert with a message param that is evaluated lazily? Thanks

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  • Scala: "using" keyword

    - by Albert Cenkier
    i've defined 'using' keyword as following: def using[A, B <: {def close(): Unit}] (closeable: B) (f: B => A): A = try { f(closeable) } finally { closeable.close() } i can use it like that: using(new PrintWriter("sample.txt")){ out => out.println("hellow world!") } now i'm curious how to define 'using' keyword to take any number of parameters, and be able to access them separately: using(new BufferedReader(new FileReader("in.txt")), new PrintWriter("out.txt")){ (in, out) => out.println(in.readLIne) }

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  • A question about Scala Objects

    - by Randin
    In the example for coding with Json using Databinder Dispatch Nathan uses an Object (Http) without a method, shown here: import dispatch._ import Http._ Http("http://www.fox.com/dollhouse/" >>> System.out ) How is he doing this?

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  • How to access "overridden" inner class in Scala?

    - by doom2.wad
    I have two traits, one extending the other, each with an inner class, one extending the other, with the same names: trait A { class X { def x() = doSomething() } } trait B extends A { class X extends super.X { override def x() = doSomethingElse() } } class C extends B { val x = new X() // here B.X is instantiated val y = new A.X() // does not compile val z = new A.this.X() // does not compile } How do I access A.X class in the C class's body? Renaming B.X not to hide A.X is not a preferred way. To make things a bit complicated, in the situation I have encountered this problem the traits have type parameters (not shown in this example).

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  • Can someone explain me implicit parameters in Scala?

    - by Oscar Reyes
    And more specifically how does the BigInt works for convert int to BigInt? In the source code it reads: ... implicit def int2bigInt(i: Int): BigInt = apply(i) ... How is this code invoked? I can understand how this other sample: "Date literals" works. In. val christmas = 24 Dec 2010 Defined by: implicit def dateLiterals(date: Int) = new { import java.util.Date def Dec(year: Int) = new Date(year, 11, date) } When int get's passed the message Dec with an int as parameter, the system looks for another method that can handle the request, in this case Dec(year:Int) Q1. Am I right in my understanding of Date literals? Q2. How does it apply to BigInt? Thanks

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  • Scala Lift - Robust method to protect files from hotlinking

    - by sirjamm
    I'm attempting to implement a way to stop hotlinking and/or un-authorised access to resources within my app. The method I'm trying to add is something I've used before in PHP apps. Basically a session is set when the page is first called. The images are added to the page via the image tag with the session value as a parameter: <img src="/files/image/[handle]?session=12345" /> When the image is requested the script checks to see if the session is set and matches the provided value. If the condition is not met the serving page returns null. Right at the end to the code I unset the session so further requests from outside the scope of the page will return null. What would be the best implementation of this method within the lift framework? Thanks in advance for any help, much appreciated :)

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