Communications of the ACM
A Metalanguage for interactive proof in LCF
POPL '78 Proceedings of the 5th ACM SIGACT-SIGPLAN symposium on Principles of programming languages
"Type-completeness" as a language principle
POPL '80 Proceedings of the 7th ACM SIGPLAN-SIGACT symposium on Principles of programming languages
Guardians and actions: linguistic support for robust, distributed programs
POPL '82 Proceedings of the 9th ACM SIGPLAN-SIGACT symposium on Principles of programming languages
On understanding types, data abstraction, and polymorphism
ACM Computing Surveys (CSUR) - The MIT Press scientific computation series
Block structure and object oriented languages
OOPWORK '86 Proceedings of the 1986 SIGPLAN workshop on Object-oriented programming
Towards a Unified Programming Language
ECOOP '00 Proceedings of the 14th European Conference on Object-Oriented Programming
NIL: An integrated language and system for distributed programming
Proceedings of the 1983 ACM SIGPLAN symposium on Programming language issues in software systems
The when, why and why not of the BETA programming language
Proceedings of the third ACM SIGPLAN conference on History of programming languages
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Ada is rich in the variety of its abstraction mechanisms. It has both a data abstraction mechanism (packages with private data types) that supports a functional programming style and a program abstraction mechanism (generic program units) that supports an object-oriented program style. Tradeoffs between data and program abstraction are examined and it is pointed out that Ada discourages program abstraction because program units are not first-class objects. It is shown how program units could be made into first-class objects by introducing closures as values for functions and records with function components as values for packages. Further unification by allowing types to be first-class objects conflicts with the requirement of compile-time type invariance. The relaxation of this requirement in a manner that preserves type consistency is examined and leads to a notion of value for types as tuples of operations. It is suggested in the conclusion that our understanding of abstraction for object-oriented languages and of other language design, implementation, and environment issues will have progressed sufficiently by 1985 to warrant the design of a successor to Ada by the late 1980s.