Scala is a Java-like programming language which unifies object-oriented and functional programming. It is a pure object-oriented language in the sense that every value is an object. Types and behavior of objects are described by classes. Classes can be composed using mixin composition. Scala is designed to work seamlessly with less pure but mainstream object-oriented languages like Java.
Scala is a functional language in the sense that every function is a value. Nesting of function definitions and higher-order functions are naturally supported. Scala also supports a general notion of pattern matching which can model the algebraic types used in many functional languages.
Scala has been designed to interoperate seamlessly with Java. Scala classes can call Java methods, create Java objects, inherit from Java classes and implement Java interfaces. None of this requires interface definitions or glue code.
Scala has been developed from 2001 in the programming methods laboratory at EPFL. Version 1.0 was released in November 2003. This document describes the second version of the language, which was released in March 2006. It acts a reference for the language definition and some core library modules. It is not intended to teach Scala or its concepts; for this there are other documents.
Scala has been a collective effort of many people. The design and the implementation of version 1.0 was completed by Philippe Altherr, Vincent Cremet, Gilles Dubochet, Burak Emir, Stéphane Micheloud, Nikolay Mihaylov, Michel Schinz, Erik Stenman, Matthias Zenger, and the author. Iulian Dragos, Gilles Dubochet, Philipp Haller, Sean McDirmid, Lex Spoon, and Geoffrey Washburn joined in the effort to develop the second version of the language and tools. Gilad Bracha, Craig Chambers, Erik Ernst, Matthias Felleisen, Shriram Krishnamurti, Gary Leavens, Sebastian Maneth, Erik Meijer, Klaus Ostermann, Didier Rémy, Mads Torgersen, and Philip Wadler have shaped the design of the language through lively and inspiring discussions and comments on previous versions of this document. The contributors to the Scala mailing list have also given very useful feedback that helped us improve the language and its tools.