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%T The Development of occam: types, classes and sharing
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%A  Geoff Barrett
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%E  Hussein S. M. Zedan
%B OUG\-13: Real\-Time Systems with Transputers
%X The proposed extensions to the occam* language are aimed at
   providing •  a more comprehensive type system•  support
   for a modular programming style•  a facility for sharing
   between processes.The type system is similar to that of many
   modern programming languages but with a careful treatment of
   union types and without recursive types.Although it is
   possible to describe shared objects in occam2, the required
   idiom has an implementation whose complexity is linear in
   the number of users. By introducing a special sort of shared
   bus of channels, this problem can be overcome.The class
   system is designed in such a way as to allow for separate
   compilation and alien code classes to be used in occam
   programs with little overhead and to provide some of the
   abstraction mechanisms which have been recognised as
   beneficial in object\-oriented languages.There are also a
   number of new language features which do not significantly
   change the nature of the language but which do enhance its
   general expressiveness.The first part of this paper presents
   proposed changes to the occam2 reference manual ([1]). The
   second part is a commentary on the decisions which had to be
   made in order to produce the proposal. The section numbers
   of the manual changes correspond to the section numbers of
   the occam2 reference manual where a \[rs] denotes a change
   to an existing section and a letter denotes the insertion of
   a new section.