http://scala.sygneca.com// 2010-09-03T00:07:16+01:00 http://scala.sygneca.com// http://scala.sygneca.com//lib/images/favicon.ico text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/alternate-lazy-values?rev=1265879458 The JDK uses AbstractQueuedSynchronizer as the basis for its high performance concurrency implementations. Here I show how lazy values can be implemented by reusing much of the JDK machinery, and hopefully therefore inheriting high performance. Fir... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/aop-style-security-check?rev=1265879458 AOP folks love their security checking – they can use an aspects to weave security checking in and around methods of an object. Here’s a sketch of how to do something similar in Scala, but with complete type safety. We group operations i... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/applet-java-and-scala?rev=1265879458 This is an example of getting a Scala applet running in your browser, and incidentally it shows with what minimal changes you can port at least simple code, from Java with. This example is from O’Reilly’s ‘Learning Java’, it ... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/arrows?rev=1265879458 NOTE: This code doesn’t seem to work any more on recent versions of Scala. See bug report. NOTE 2: c. 2008-05-12, this code worked as-is with the 2.7.0 Eclipse plugin without exceptions. The output looked reasonable at first glance, although ... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/as-patterns?rev=1265879458 object Tails { // Finds all 'tails' of a list def tails[A](xs: List[A]): List[List[A]] = xs match { case Nil => Nil :: Nil // The as-pattern is denoted here using @ // <identifier> @ ... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/automata?rev=1265879458 Scala’s standard library has pattern matching automata built into it. There’s not much documented, so here’s some code that calls it: package regex;   import Console.println import scala.util.automata._ import scala.util.rege... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/automatic-differentiation?rev=1265879458 In the code below, we generate a function representing the second derivative of (x + 2.) * (x + 1.), and calculate the value when x = 3. For some background, see Automatic Differentiation This example will not work with release 2.7.0 or earlier. B... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/compressed-executable-jar?rev=1265879458 This is not a Scala code example, but rather a method for reducing the size of a deployed Scala application. The current Scala runtime library runs about 1.3mb, and your application’s JAR will come on top of that. I use this little program to... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/constructors?rev=1265879458 In Scala, all classes have a primary constructor, specified directly after the class name: class Test (x: Int, y: Int) { ... } Code to further initialize the object goes right into the body of the class: class Test (x: Int, ... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/defining-bean-properties?rev=1265879458 Scala provides a convenient shortcut to define bean properties (as we like to call the things that have setX and getX methods and are accessed by reflection), which are used by many Java tools import scala.reflect.BeanProperty   class Pilot&#40... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/design-by-contract?rev=1265879458 Design by Contract is a technique for designing interfaces that specify pre and post conditions on methods and invariants on objects. Playing around with some of Scala’s features that support extensibility, I implemented pre and post condition... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/finger-trees?rev=1265879458 Finger Trees are a efficient, general purpose immutable data structures that use recursive type definitions to enforce the valid state of the tree. The “fingers” of the tree structure forms that vary between one and four entries, which a... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/futures?rev=1265879458 Can somebody write an explanation about this? The code and the comments do not help much. Sure :) I should have in the first place. Refer to Alice ML’s description of futures (http://www.ps.uni-sb.de/alice/manual/futures.html) for detaile... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/gps?rev=1265879458 Lisp code for comparison by Peter Norvig here. package gps object gps2 { import Utilities._ // debug stuff and port of Lisp "some" function /** a condition that holds or does not hold * In the Lisp version there are two types of c... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/graphviz-dot-parser?rev=1265879458 Having lots of examples for parsing code is a good idea, because it can be pretty tricky to understand at times...this is a rough cut of a parser for the DOT language, used by the GraphViz program. DotParser.scala: package scaladot;   import s... text/html 2010-02-28T16:13:52+01:00 http://scala.sygneca.com//code/hello-swing?rev=1267373632 import javax.swing._ object HelloWorld extends JFrame( "Greetings" ) { def main( args: Array[String] ) = { setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE ) add( new JLabel( "Hello World" ) ) pack() setVisibl... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/integrating-with-jaxen?rev=1265879458 Jaxen is a Java library providing generic navigation via xpath across various kinds of object/document models. Here’s how to integrate it with Scala, which gives you the ability to use xpath to navigate through (and filter) Scala objects. pac... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/javavarargs?rev=1265879458 In http://lampsvn.epfl.ch/trac/scala/ticket/1342, mustaghattack submitted the following test cases: File scala/ticket1342/JavaVarArgsInterface.java: package scala.ticket1342; interface JavaVarArgsInterface { void varArgsMethod( String ... args );... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/jaxb-schemagen?rev=1265879458 JAXB schemagen automatically creates XML Schemas from JavaBeans. Scala can create JavaBeans, and now that it has the ability to attach JDK 1.5 annotations, it can be used with schemagen. package com.soletta.lb;   import javax.xml.bind.annotatio... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/junit-tests?rev=1265879458 Scala works fine with the JUnit testing framework. You simply use the Java interfaces and classes, just as if you were writing the tests in Java. As an example, here is an individual test case that works with JUnit 3.8. Note that you can import all... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/mini-kanren?rev=1265879458 Here’s a simple Scala version of the Mini Kanren, the logic programming core used in the book “The Reasoned Schemer”. The core is less than 100 lines of code. It makes use of a number of Scala features, like case classes, functions... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/minimax-analysis?rev=1265879458 Here’s an abstract framework for minimax analysis of two-player zero-sum games with perfect information. package zerosum   /** * The GameState trait represents an immutable game state that can be analyzed * by a search algorithm. * * @au... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/particle-swarm-optimization?rev=1265879458 This little example puts together previously introduced ideas about Scala and tries to show a non-trivial algorithm. It is a basic implementation of an optimization algorithm called particle swarm optimization. See Wikipedia's page on the topic for ... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/probabilistic-modeling?rev=1265879458 For my induction into Scala, I wanted to translate the probabilistic monad of Chapter 9 of Expert F# (Introducing Language-Oriented Programming). The idea, based on the paper Stochastic Lambda Calculus and Monads of Probability Distributions, is to ... text/html 2010-05-29T18:06:11+01:00 http://scala.sygneca.com//code/remoteactors?rev=1275152771 I made a few patches to the example from http://dirkmeister.blogspot.com/2008/12/remote-actors-in-scala.html. It works with Scala 2.7.4RC1 on ubuntu 8.10. Milage may vary. RemotePongApp must be started first. RemotePingApp.scala: package mgm7734 &... text/html 2010-07-18T15:24:44+01:00 http://scala.sygneca.com//code/scalagui?rev=1279463084 A Scala framework wrapping Swing. It uses event loops to solve the inversion-of-control problem of Swing’s callback events. It uses multiple-inheritance for clean composition of widget properties. It uses Scala’s capability for embed... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/shared-objects?rev=1265879458 This demonstrates an approach to shared objects, and shows how to work with abstract types as well. Note that this is a work-in-progress posted for comment! package scalax.shared;   /** We provide a default shared factory object. This code is i... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/sidebar?rev=1265879458 Code examples Examples list Scala features GraphViz DOT Parser AOP Style Security Check Subversion Fast Update XML Pattern Matching As-Patterns Automata Arrows Verbatim filter Constructors Design By Contract Automatic Differentiation ... text/html 2010-07-09T06:23:58+01:00 http://scala.sygneca.com//code/simplifying-jdbc?rev=1278653038 Scala’s syntax can make typing-intensive tasks a lot easier to handle. Here’s one way to “Scalify” a Java library. I make liberal use of operators and implicit conversions to achieve a terse and readable syntax for handling J... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/software-transactional-memory?rev=1265879458 The facilities provided here are modelled on the Haskell STM facilities described in Composable memory transactions, by Tim Harris, Simon Marlow, Simon Peyton Jones, and Maurice Herlihy, in ACM Conference on Principles and Practice of Parallel Prog... text/html 2010-08-19T17:59:48+01:00 http://scala.sygneca.com//code/start?rev=1282237188 Code Examples Scala features GraphViz DOT Parser - Shows how to construct a parser for the DOT language with Scala’s combinator parsers AOP Style Security Check - Using Scala’s implicit values and coercions to do AOP-like securit... text/html 2010-04-09T21:18:54+01:00 http://scala.sygneca.com//code/step-1?rev=1270844334 /* So, you've heard about Scala. It's a cool functional language that compiles down to Java byte-code and looks and acts like a Java program. You've looked at some documentation and saw stuff like "higher order functions" and other stuff th... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/step-2?rev=1265879458 /* So, you've heard about Scala. It's a cool functional language that compiles down to Java byte-code and looks and acts like a Java program. You've looked at some documentation and saw stuff like "higher order functions" and other stuff th... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/subversion-fast-update?rev=1265879458 At my office we’ve got a wide (many projects) and large (tons of stuff) subversion repository. The svn tool can take upwards of five minutes to perform an update against a branch of the repository. svn does a nice job of emitting xml output if... text/html 2010-08-31T13:10:48+01:00 http://scala.sygneca.com//code/sudoku?rev=1283256648 object SudokuSolver extends Application { // The board is represented by an array of strings (arrays of chars), // held in a global variable m. The program begins by reading 9 lines // of input to fill the board var m: Array[Array[Ch... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/verbatim-filter?rev=1265879458 By Martin Odersky The following program formats Scala code embedded in LaTeX files. It translates all sections in a LaTeX source which are delimited by \verb@...@ or by \begin{verbatim} ... \end{verbatim}. The translation maps into environment... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/wrapping-jmx?rev=1265879458 This example wraps some common JMX idioms, enabling nice pattern-matching across JMX-derived information. package com.soletta.spipe;   import javax.management._; import java.lang.management._;   object SJMX { val mbeanServer = Mana... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//code/xml-pattern-matching?rev=1265879458 Below you’ll find three different ways of pattern matching XML data within Scala. XML is a first-class entity within Scala; you write XML directly in your source code and the Scala compiler will replace it with correctly-typed objects from the...