University of Utah
                   Department of Computer Science

                           UUCS-92-007



               The Programming Language Jigsaw:
           Mixins, Modularity and Multiple Inheritance

                            Gilad Bracha

                             Abstract

   This dissertation provides a framework for modularity in programming lan-
guages. In this framework, known as Jigsaw, inheritance is understood to be an
essential linguistic mechanism for module manipulation.
   In Jigsaw, the roles of classes in existing languages are "unbundled", by
providing a suite of operators independently controlling such effects as combi-
nation, modification, encapsulation, name resolution, and sharing, all on the
single notion of module.
   All module operators are forms of inheritance. Thus, inheritance is not in
conflict with modularity in this system, but is indeed its foundation.
   This allows a previously unobtainable spectrum of features to be combined
in a cohesive manner, including multiple inheritance, mixins, encapsulation and
strong typing.
   Jigsaw has a rigorous semantics, based upon a denotational model of 
inheritance.
   Jigsaw provides a notion of modularity independent of a particular 
computational paradigm. Jigsaw can therefore be applied to a wide variety of 
languages, especially special-purpose languages where the effort of designing 
specific mechanisms for modularity is difficult to justify, but which could 
still benefit from such mechanisms.
   The framework is used to derive an extension of Modula-3 that supports
the new operations. An efficient implementation strategy is developed for this
extension. The performance of this scheme is on a par with the methods em-
ployed by the highest performance object-oriented language processors currently
available.