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diff --git a/doc/reference/rationale-chapter.verb.tex b/doc/reference/rationale-chapter.verb.tex index 565a09e956..666e20753b 100644 --- a/doc/reference/rationale-chapter.verb.tex +++ b/doc/reference/rationale-chapter.verb.tex @@ -65,37 +65,21 @@ paradigms within the language itself. The benefits of integration are realized fully only if the common language achieves a meaningful unification of concepts rather than being merely an agglutination of different programming paradigms. This is what we try to achieve with -Scala\footnote{Scala stands for ``Software Composition and -Architecture LAnguage''.}. +Scala\footnote{Scala stands for ``Scalable Language''.}. -Scala is an object-oriented and functional language with clear -semantic foundations. -\begin{itemize} -\item[] {\em Object-oriented:} -Scala 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 interact well with mainstream object-oriented -languages, in particular Java and C\#. -\item[] {\em Functional:} -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. -%\item[] {\em Concurrent:} -%Scala is a concurrent language in the sense that it supports -%lightweight threads with flexible constructs for message passing and -%process synchronization. These constructs are based functional nets, a -%theory which combines the principles of functional programming and -%Petri nets in a small kernel language based on Join calculus. -\item[] {\em Clear semantic foundations:} -The operational semantics of a Scala program can be formulated as a -functional net. Scala has an expressive type system which combines -genericity, subtyping, and a form of intersection types based on mixin -classes. That type system is in turn based on the foundational type -theory of name dependent types. -\end{itemize} +Scala is both an an object-oriented and functional language. 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 interact well with mainstream object-oriented languages, +in particular Java and C\#. + +Scala is also 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. Furthermore, this notion of pattern matching +naturally extends to the processing of XML data. The design of Scala is driven by the desire to unify object-oriented and functional elements. Here are three examples how this is achieved: @@ -119,24 +103,19 @@ This can express both closed and extensible data types, and also provides a convenient way to exploit run-time type information in cases where static typing is too restrictive. \item -Software architecture languages are often based on a formalized notion -of component. A component can be expressed in Scala as a mixin class -where provided services are defined fields and required services are -abstract fields. Components are assembled using mixin composition. To -make this work in all contexts, defined service fields need to be -constructed lazily on demand. This component/composition design -pattern relies in an essential way on the object-oriented concept of -mixin composition and the functional concept of lazy evaluation. +Module systems of functional languages such as SML or Caml excel in +abstraction; they allow very precise control over visibility of names +and types, including the ability to partially abstract over types. By +contrast, object-oriented languages excell in composition; they offer +several composition mechanisms lacking in module systems, including +inheritance and unlimited recursion between objects and classes. +Scala unifies the notions of object and module, of module signature +and interface, as well as of functor and class. This combines the +abstraction facilities of functional module systems with the +composition constructs of object-oriented languages. The unification +is made possible by means of a new type system based on path-dependent +types \cite{odersky-et-al:fool10}. \end{itemize} -%The theory of functional nets lets us describe both functional and -%concurrent computations in one reduction rule. Mutable variables can -%be described as special cases of concurrent computations, where a -%variable acts as a concurrent thread that keeps a variable's value -%until the next write operation. Thereby, a conceptual unification of -%the theories underlying functions, state, and concurrency is -%established. The unified theory does not preclude Scala compilers to -%choose specialized, more efficient implementation techniques, however. -%\end{itemize} %The rest of this report is structured as follows. Chapters %\ref{sec:simple-examples} to \ref{sec:concurrency} give an informal overview of @@ -144,6 +123,3 @@ mixin composition and the functional concept of lazy evaluation. %chapters contain the language definition. The definition is formulated %in prose but tries to be precise. -At present the report is still preliminary. Many examples remain to be filled -in, and the definition needs to be made more precise and legible. I am grateful -for all comments that help improve it. |