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  • How do Scala parser combinators compare to Haskell's Parsec?

    - by artif
    I have read that Haskell parser combinators (in Parsec) can parse context sensitive grammars. Is this also true for Scala parser combinators? If so, is this what the "into" (aka "") function is for? What are some strengths/weaknesses of Scala's implementation of parser combinators, vs Haskell's? Do they accept the same class of grammars? Is it easier to generate error messages or do other miscellaneous useful things with one or the other? How does packrat parsing (introduced in Scala 2.8) fit into this picture? Is there a webpage or some other resource that shows how different operators/functions/DSL-sugar from one language's implementation maps onto the other's?

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  • How to customize Json serialization using Scala and Play Framework?

    - by Jonas
    I would like to serialize some Scala case classes to Json. E.g my case class looks like: case class Item ( id: Int, name: String, price: BigDecimal, created: java.util.Date) and I would like to serialize it to Json like this: {"id":3, "name": "apple", "price": 8.00, "created": 123424434} so I need a custom serilization for BigDecimal and for Date. Where I want the data in milliseconds since 1 jan 1970. When using Scala and Play Framework, I can return Json using Json(myObject), but how do I customize the serialization? Or is there any recommended Scala library?

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  • How to check whether a String fully matches a Regex in Scala?

    - by mkneissl
    Assume I have a Regex pattern I want to match many Strings to. val Digit = """\d""".r I just want to check whether a given String fully matches the Regex. What is a good and idiomatic way to do this in Scala? I know that I can pattern match on Regexes, but this is syntactically not very pleasing in this case, because I have no groups to extract: scala> "5" match { case Digit() => true case _ => false } res4: Boolean = true Or I could fall back to the underlying Java pattern: scala> Digit.pattern.matcher("5").matches res6: Boolean = true which is not elegant, either. Is there a better solution?

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  • How do I return a String from a for comprehension in Scala?

    - by Vonn
    Scala Newbie alert: basically I'm trying to do something like this: where I pattern match and return a String. scala> def processList(list: List[String], m: String): String={list foreach (x=> m match{ | case "test" => "we got test" | case "test1"=> "we got test1"})} :10: error: type mismatch; found : Unit required: String def processList(list: List[String], m: String): String={list foreach (x= m match{ I know I can set a var and return it after the for comp... but that doesn't seem to be the Scala way.

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  • Strange Play Framework 2.2 exceptions after trying to add MySQL / slick

    - by Mike Cialowicz
    I'm working on a Play 2.2 application, and things have gone a bit south on me since I've tried adding my DB layer. Below are my build.sbt dependencies. As you can see I use mysql-connector-java and play-slick: libraryDependencies ++= Seq( jdbc, anorm, cache, "joda-time" % "joda-time" % "2.3", "mysql" % "mysql-connector-java" % "5.1.26", "com.typesafe.play" %% "play-slick" % "0.5.0.8", "com.aetrion.flickr" % "flickrapi" % "1.1" ) My application.conf has some similarly simple DB stuff in it: db.default.url="jdbc:mysql://localhost/myDb" db.default.driver="com.mysql.jdbc.Driver" db.default.user="root" db.default.pass="" This is what it looks like when my Play server starts: [info] play - Listening for HTTP on /0:0:0:0:0:0:0:0:9000 (Server started, use Ctrl+D to stop and go back to the console...) [info] Compiling 1 Scala source to C:\bbq\cats\in\space [info] play - database [default] connected at jdbc:mysql://localhost/myDb [info] play - Application started (Dev) So, it appears that Play can connect to the MySQL DB just fine (I think). However, I get this exception when I make any request to my server: [error] p.nettyException - Exception caught in Netty java.lang.NoSuchMethodError: akka.actor.ActorSystem.dispatcher()Lscala/concurren t/ExecutionContext; at play.core.Invoker$.<init>(Invoker.scala:24) ~[play_2.10.jar:2.2.0] at play.core.Invoker$.<clinit>(Invoker.scala) ~[play_2.10.jar:2.2.0] at play.api.libs.concurrent.Execution$Implicits$.defaultContext$lzycompu te(Execution.scala:7) ~[play_2.10.jar:2.2.0] at play.api.libs.concurrent.Execution$Implicits$.defaultContext(Executio n.scala:6) ~[play_2.10.jar:2.2.0] at play.api.libs.concurrent.Execution$.<init>(Execution.scala:10) ~[play _2.10.jar:2.2.0] at play.api.libs.concurrent.Execution$.<clinit>(Execution.scala) ~[play_ 2.10.jar:2.2.0] The odd thing is that the 2nd request (to the exact same URL, same controller, no changes) comes back with a different error: [error] p.nettyException - Exception caught in Netty java.lang.NoClassDefFoundError: Could not initialize class play.api.libs.concurr ent.Execution$ at play.core.server.netty.PlayDefaultUpstreamHandler.handleAction$1(Play DefaultUpstreamHandler.scala:194) ~[play_2.10.jar:2.2.0] at play.core.server.netty.PlayDefaultUpstreamHandler.messageReceived(Pla yDefaultUpstreamHandler.scala:169) ~[play_2.10.jar:2.2.0] at com.typesafe.netty.http.pipelining.HttpPipeliningHandler.messageRecei ved(HttpPipeliningHandler.java:62) ~[netty-http-pipelining.jar:na] at org.jboss.netty.handler.codec.http.HttpContentDecoder.messageReceived (HttpContentDecoder.java:108) ~[netty-3.6.5.Final.jar:na] at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:29 6) ~[netty-3.6.5.Final.jar:na] at org.jboss.netty.handler.codec.frame.FrameDecoder.unfoldAndFireMessage Received(FrameDecoder.java:459) ~[netty-3.6.5.Final.jar:na] The URL / controller that I'm requesting just renders a static web page and doesn't do anything of any significance. It was working just fine before I started adding my DB layer. I'm rather stuck. Any help would be greatly appreciated, thanks. I'm using Scala 2.10.2, Play 2.2.0, and MySQL Server 5.6.14.0 (community edition).

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  • scalacheck/scalatest not found: how to add it in sbt/scala?

    - by Pavel Reich
    I've installed typesafe-stack from http://typesafe.com/stack/download on my ubuntu12, than I created a play project (g8 typesafehub/play-scala) and now I want to add scalatest or scalacheck to my project. So my_app/project/plugins.sbt has the following lines: // The Typesafe repository resolvers += "Typesafe repository" at "http://repo.typesafe.com/typesafe/releases/" // Use the Play sbt plugin for Play projects addSbtPlugin("play" % "sbt-plugin" % "2.0.1") Then I added scalatest using addSbtPlugin: addSbtPlugin("org.scalatest" %% "scalatest" % "2.0.M1" % "test") and now it fails with the following message when I run 'sbt test' [info] Resolving org.scalatest#scalatest;2.0.M1 ... [warn] module not found: org.scalatest#scalatest;2.0.M1 [warn] ==== typesafe-ivy-releases: tried [warn] http://repo.typesafe.com/typesafe/ivy-releases/org.scalatest/scalatest/scala_2.9.1/sbt_0.11.3/2.0.M1/ivys/ivy.xml [warn] ==== local: tried [warn] ~/.ivy2/local/org.scalatest/scalatest/scala_2.9.1/sbt_0.11.3/2.0.M1/ivys/ivy.xml [warn] ==== Typesafe repository: tried [warn] http://repo.typesafe.com/typesafe/releases/org/scalatest/scalatest_2.9.1_0.11.3/2.0.M1/scalatest-2.0.M1.pom [warn] ==== typesafe-ivy-releases: tried [warn] http://repo.typesafe.com/typesafe/ivy- releases/org.scalatest/scalatest/scala_2.9.1/sbt_0.11.3/2.0.M1/ivys/ivy.xml [warn] ==== public: tried [warn] http://repo1.maven.org/maven2/org/scalatest/scalatest_2.9.1_0.11.3/2.0.M1/scalatest-2.0.M1.pom What I don't understand: why does it use this http://repo.typesafe.com/typesafe/releases/org/scalatest/scalatest_2.9.1_0.11.3/2.0.M1/scalatest-2.0.M1.pom URL instead of the real one http://repo.typesafe.com/typesafe/releases/org/scalatest/scalatest_2.9.1/2.0.M1/scalatest_2.9.1-2.0.M1.pom? Quite the same problem I have with scalacheck: it also tries to download using sbt-version specific artifactId whereas the repository has only scala-version specific. What am I doing wrong? I understand there must be a switch in sbt somewhere, not to use sbt-version as part of the artifact URL? I also tried using this in my plugins.sbt libraryDependencies += "org.scalatest" %% "scalatest" % "2.0.M1" % "test" but looks like it is completely ignored by sbt and scalatest.jar hasn't appeared in the classpath: my_app/test/AppTest.scala:1: object scalatest is not a member of package org [error] import org.scalatest.FunSuite because the output of sbt clean && sbt test has lots of Resolving org.easytesting#fest-util;1.1.6 or just another library, but nothing about scalatest. I use scala 2.9.1 and sbt 0.11.3, trying to use scalatest 2.0.M1 and 1.8; scalacheck: resolvers ++= Seq( "snapshots" at "http://oss.sonatype.org/content/repositories/snapshots", "releases" at "http://oss.sonatype.org/content/repositories/releases" ) libraryDependencies ++= Seq( "org.scalacheck" %% "scalacheck" % "1.9" % "test" ) With the same outcome, i.e. it uses the sbtVersion specific POM URL, which doesn't exist. What am I doing wrong? Thanks.

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  • Are there any tools for performing static analysis of Scala code?

    - by Roman Kagan
    Are there any tools for performing static analysis of Scala code, similar to FindBugs and PMD for Java or Splint for C/C++? I know that FindBugs works on the bytecode produced by compiling Java, so I'm curious as to how it would work on Scala. Google searches (as of 27 October 2009) reveal very little. Google searches (as of 01 February 2010) reveal this question.

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  • Has anyone got the vim taglist plugin working with Scala?

    - by Eric Hauser
    I'm having trouble getting the taglist plugin working properly with Scala. I've installed the plugin and ctags and verified that it works properly with Java and C++. I then followed the instructions on this page (minus the Lift specific instructuions), but was nothing shows up in the taglist window when I open it while editing a Scala file. Has anyone got this working and what are the proper steps? Thanks.

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  • How to store date into Mysql database with play framework in scala?

    - by Rahul Kulhari
    I am working with play framework with scala and what am i doing : login page to login into web app sign up page to register into web app after login i want to store all databases values to user what i want to do: when user register for web app then i want to store user values into database with current time and date but my form is giving error. error: List(FormError(dates,error.required,List())),None) controllers/Application.scala object Application extends Controller { val ta:Form[Keyword] = Form( mapping( "id" -> ignored(NotAssigned:Pk[Long]), "word" -> nonEmptyText, "blog" -> nonEmptyText, "cat" -> nonEmptyText, "score"-> of[Long], "summaryId"-> nonEmptyText, "dates" -> date("yyyy-MM-dd HH:mm:ss") )(Keyword.apply)(Keyword.unapply) ) def index = Action { Ok(html.index(ta)); } def newTask= Action { implicit request => ta.bindFromRequest.fold( errors => {println(errors) BadRequest(html.index(errors))}, keywo => { Keyword.create(keywo) Ok(views.html.data(Keyword.all())) } ) } models/keyword.scala case class Keyword(id: Pk[Long],word: String,blog: String,cat: String,score: Long, summaryId: String,dates: Date ) object Keyword { val keyw = { get[Pk[Long]]("keyword.id") ~ get[String]("keyword.word")~ get[String]("keyword.blog")~ get[String]("keyword.cat")~ get[Long]("keyword.score") ~ get[String]("keyword.summaryId")~ get[Date]("keyword.dates") map { case id~blog~cat~word~score~summaryId~dates => Keyword(id,word,blog,cat,score, summaryId,dates) } } def all(): List[Keyword] = DB.withConnection { implicit c => SQL("select * from keyword").as(Keyword.keyw *) } def create(key: Keyword){DB.withConnection{implicit c=> SQL("insert into keyword values({word},{blog}, {cat}, {score},{summaryId},{dates})").on('word-> key.word,'blog->key.blog, 'cat -> key.cat, 'score-> key.score, 'summaryId -> key.summaryId, 'dates->new Date()).executeUpdate } } views/index.scala.html @(taskForm: Form[Keyword]) @import helper._ @main("Todo list") { @form(routes.Application.newTask) { @inputText(taskForm("word")) @inputText(taskForm("blog")) @inputText(taskForm("cat")) @inputText(taskForm("score")) @inputText(taskForm("summaryId")) <input type="submit"> <a href="">Go Back</a> } } please give me some idea to store date into mysql databse and date is not a field of form

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  • How do I provide basic configuration for a Scala application?

    - by Dave
    I am working on a small GUI application written in Scala. There are a few settings that the user will set in the GUI and I want them to persist between program executions. Basically I want a scala.collections.mutable.Map that automatically persists to a file when modified. This seems like it must be a common problem, but I have been unable to find a lightweight solution. How is this problem typically solved?

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  • Installing a VADTools design component into your 3CX Voice Application Designer toolbox

    - by ParadigmShift
    The 3CX Voice Application Designer is an innovative tool for creating IVR (Interactive Voice Response) Applications, or Voice Applications.  It is a familiar drag-and-drop experience that Visual Studio developers will get the hang of pretty quick. Additionally, there are new 3rd party components released by BlueVoice, that are distributed though www.UtahVoIPStore.com I thought I’d post a quick introduction to it, by showing how to install a component into you designer tool box.  In this example I am using the CommandLine component, which lets you call the command line from your voice application. First, copy the ZIP file that came with your component to the root folder of your VAD project. Now extract the zip file into the root directory. The component will be in the root directory and the Libraries directory will have a new DLL file. Open your VAD project and right-click on the project in project explorer to add the new component to your project. Navigate to the root folder of your project and select the new component. The component is now ready for you to use in your toolbox.

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  • Visual web page designer for Django?

    - by Robert Oschler
    I'm just starting my Django learning so pardon me if any part of this question is off-base. I have done a lot of web searching for information on the equivalent of a visual web page designer for Django and I don't seem to be getting very far. I have experience with Delphi (Object Pascal), C, C++, Python, PHP, Java, and Javascript and have created and maintained several web sites that included MySQL database dependent content. For the longest time I've been using one of the standard WYSIWIG designers to design the actual web pages, with any needed back end programming done via Forms or AJAX calls that call server side PHP scripts. I have grown tired of the quirks, bugs, and other annoyances associated with the program. Also, I find myself hungry for the functionality and reliability a good MVC based framework would provide me so I could really express myself with custom code easily. So I am turning to Django/Python. However, I'm still a junkie for a good WYSIWIG designer for the layout of web pages. I know there are some out there that thrive on opening up a text editor, possibly with some code editor tools to assist, and pounding out pages. But I do adore a drag and drop editor for simple page layout, especially for things like embedded images, tables, buttons, etc. I found a few open source projects on GitHub but they seem to be focused on HTML web forms, not a generic web page editor. So can I get what I want here? The supreme goal would be to find not only a web page editor that creates Django compatible web pages, but if I dare say it, have a design editor that could add Python code stubs to various page elements in the style of the Delph/VCL or VB design editors. Note, I also have the Wing IDE Professional IDE, version 2.0. As a side note, if you know of any really cool, fun, or time-saving Python libraries that are designed for easy integration into Django please tell me about them. -- roschler

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  • Can I become a Game Designer? [on hold]

    - by user32721
    This is my first time posting something on a forum in 4 years. I am posting this because I want to adjust my expectations and goals regarding game design. I am in college in Morocco (Al Akhawayn university). just started my junior year. I am a communications major (school of humanities) and a gender studies minor. I want to become a video game designer. It is the only career that I am interested in. I have been playing ever since I was 5 and haven't stopped yet. Currently I don't have any noteworthy skills to become a designer. I don't know how to program (don't really have the patience for it) and I can't draw to save my life. I haven't tried visual software like MAYA or MAX so I can't comment on graphic design. So I basically want to know whether my current education is capable of helping me reach my goal. If not then should I take a master's in game design (in the U.S?) or switch my minor to computer science? I am sorry that this post is long! I look forward to hearing your advice!

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  • What type of webapp is the sweet spot for Scala's Lift framework?

    - by ajay
    What kind of applications are the sweet spot for Scala's lift web framework. My requirements: Ease of development and maintainability Ready for production purposes. i.e. good active online community, regular patches and updates for security and performance fixes etc. Framework should survive a few years. I don't want to write a app in a framework for which no updates/patches are available after 1 year. Has good UI templating engines Interoperation with Java (Scala satisfies this arleady. Just mentioning here for completeness sake) Good component oriented development. Time required to develop should be proportion to the complexity of web application. Should not be totally configuration based. I hate it when code gets automatically generated for me and does all sorts of magic under the hood. That is a debugging nightmare. Amount of Lift knowledge required to develop a webapp should be proportional to the complexity of the web application. i.e I should't have to spend 10+ hours learning Lift just to develop a simple TODO application. (I have knowledge of Databases, Scala) Does Lift satisfy these requirements?

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  • Why would a variable in Scala code mysteriously become null?

    - by Alex R
    I've isolated the problem down to this: Predef.println("the value of argv1 here is " + argv(1)); var n: $ = undef; n = argv(1); Predef.println("the value of argv1 here is " + argv(1)); Predef.println("the value of n here is " + n); Predef.println("the class of n here is " + n.getClass); Here's the definition of $: class $ { println("constructed a new $ of type: " + this.getClass); def value: $ = this; def toValue: Value = { new ConstStringValue(this.toString()) }; def -(sym: Symbol): $ = { println("looked up: " + sym); this } def -(sym: $): $ = { println("looked up: " + sym); this } def update(sym: Symbol, any: Any) { println("update called: " + sym + "=" + any); } def apply(sym: Symbol) = { this } def apply(obj: $) = { this } def apply() = { this } def +(o:$) = this.toValue.div(o.toValue) def *(o:$) = this.toValue.mul(o.toValue) def >(o:$) = this.toValue.gt(o.toValue) def <(o:$) = this.toValue.lt(o.toValue) def ++() = { this } def -=(o:$) = { this } } When run, the code prints: the value of argv1 here is 10 the value of argv1 here is 10 the value of n here is null java.lang.NullPointerException at test_1_php$.include(_tmp.scala:149) at php.script.main(php.scala:57) at test_1_php.main(_tmp.scala) [...] Why would n mysteriously lose its value (or fail to take one on)?

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  • WANT TO host Visual Studio Form Designer in my own application..

    - by this. __curious_geek
    Hi, I'm writing an application that lets the end use design a Form just the way Visual Studio lets you design a windows forms. I looked into visual studio forms designer articles in msdn and also studied open-source SharpDevelop editor. Both the examples host visual studio's windows forms designer to provide form-design service in their respective applications. My question is - Does it imply any licensing issue with Microsoft for directly hosting their Visual Studio Forms designer in my own application ? I don't want move ahead without proper and correct information. Can anybody here help me out if there's any licensing issues in case I want to host visual studio windows fomr designer in my own application. If there's any such licensing implication - then how does Sharp-Develop do this ?

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  • Why does one of these statements compile in Scala but not the other?

    - by Jeff
    (Note: I'm using Scala 2.7.7 here, not 2.8). I'm doing something pretty simple -- creating a map based on the values in a simple, 2-column CSV file -- and I've completed it easily enough, but I'm perplexed at why my first attempt didn't compile. Here's the code: // Returns Iterator[String] private def getLines = Source.fromFile(csvFilePath).getLines // This doesn't compile: def mapping: Map[String,String] = { Map(getLines map { line: String => val pairArr = line.split(",") pairArr(0) -> pairArr(1).trim() }.toList:_*) } // This DOES compile def mapping: Map[String,String] = { def strPair(line: String): (String,String) = { val pairArr = line.split(",") pairArr(0) -> pairArr(1).trim() } Map(getLines.map( strPair(_) ).toList:_*) } The compiler error is CsvReader.scala:16: error: value toList is not a member of (St ring) = (java.lang.String, java.lang.String) [scalac] possible cause: maybe a semicolon is missing before `value toList'? [scalac] }.toList:_*) [scalac] ^ [scalac] one error found So what gives? They seem like they should be equivalent to me, apart from the explicit function definition (vs. anonymous in the nonworking example) and () vs. {}. If I replace the curly braces with parentheses in the nonworking example, the error is "';' expected, but 'val' found." But if I remove the local variable definition and split the string twice AND use parens instead of curly braces, it compiles. Can someone explain this difference to me, preferably with a link to Scala docs explaining the difference between parens and curly braces when used to surround method arguments?

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  • How Does One Make Scala Control Abstraction in Repeat Until?

    - by peter_pilgrim
    Hi I am Peter Pilgrim. I watched Martin Odersky create a control abstraction in Scala. However I can not yet seem to repeat it inside IntelliJ IDEA 9. Is it the IDE? package demo class Control { def repeatLoop ( body: = Unit ) = new Until( body ) class Until( body: = Unit ) { def until( cond: = Boolean ) { body; val value: Boolean = cond; println("value="+value) if ( value ) repeatLoop(body).until(cond) // if (cond) until(cond) } } def doTest2(): Unit = { var y: Int = 1 println("testing ... repeatUntil() control structure") repeatLoop { println("found y="+y) y = y + 1 } { until ( y < 10 ) } } } The error message reads: Information:Compilation completed with 1 error and 0 warnings Information:1 error Information:0 warnings C:\Users\Peter\IdeaProjects\HelloWord\src\demo\Control.scala Error:Error:line (57)error: Control.this.repeatLoop({ scala.this.Predef.println("found y=".+(y)); y = y.+(1) }) of type Control.this.Until does not take parameters repeatLoop { In the curried function the body can be thought to return an expression (the value of y+1) however the declaration body parameter of repeatUntil clearly says this can be ignored or not? What does the error mean?

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  • If I can host Visual Studio Form Designer in my application..

    - by this. __curious_geek
    Hi, I'm writing an application that lets the end use design a Form just the way Visual Studio lets you design a windows forms. I looked into visual studio forms designer articles in msdn and also studied open-source SharpDevelop editor. Both the examples host visual studio's windows forms designer to provide form-design service in their respective applications. My question is - Does it imply any licensing issue with Microsoft for directly hosting their Visual Studio Forms designer in my own application ? I don't want move ahead without proper and correct information. Can anybody here help me out if there's any licensing issues in case I want to host visual studio windows fomr designer in my own application. If there's any such licensing implication - then how does Sharp-Develop do this ?

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  • Is there a Scala version of .irbrc or another way to define some default libraries for REPL use?

    - by Tom Morris
    I've written a little library that uses implicits to add functionality that one only needs when using the REPL in Scala. Ruby has libraries like this - for things like pretty printing, firing up text editors (like the interactive_editor gem which invokes Vim from irb - see this post), debuggers and the like. The library I am trying to write adds some methods to java.lang.Class and java.lang.reflect classes using the 'pimp my library' implicit conversion process to help you go and find documentation (initially, with Google, then later possibly with a JavaDoc/ScalaDoc viewer, and maybe the StackOverflow API eventually!). It's an itch-scratching library: I spend so much time copying and pasting classnames into Google that I figured I may as well automate the process. It is the sort of functionality that developers will want to add to their system for use only in the REPL - they shouldn't really be adding it to projects (partly because it may not be something that their fellow developers want, but also because if you are doing some exploratory development, it may be with just a Scala REPL that's not being invoked by an IDE or build tool). In my case, I want to include a few classes and set up some implicits - include a .jar on the CLASSPATH and import it, basically. In Ruby, this is the sort of thing that you'd add to your .irbrc file. Other REPLs have similar ways of setting options and importing libraries. Is there a similar file or way of doing this for the Scala REPL?

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