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One of the major problems in cooperative software development is that of maintaining certain global consistency properties.Broadcasting changes that have already occured, as many programming environments do, will not resolve this problem.We argue in favor of an architecture where the announcements deal with impending or proposed changes as well as changes that have already occurred.One can then formulate consistency requirements on the system that are maintained "lazily" as it evolves.Such an architecture can support a wider range of cooperative processes than traditional software development environments.This paper describes the design and implementation of this architect ure.

The process of developing and evolving complex software systems is intrinsically exploratory in nature.Some prototyping activity is therefore inevitable in every stage of that process.Our program development and evolution methodology is predicated upon this observation.In this methodology, a prototype software system is developed as an approximation to an envisioned target system by compromising along one or more of the following dimensions: system performance, system functionality, or user interface.However, the prototype is not the end-product of the process.Instead, we support iterative evolution of the prototype towards the envisioned system by gradually dealing with the three general areaa of compromise.This paper describes the methodology of using this alternative lifecycle; to wit, the programming language concepts and related implementation technology that support practice of the suggested methodology.We summarize the lessons we have learned in building and using this technology over the last several years.