0.0.0.9 1.4.9 Simplicity.

In the early days of the Ada project, a general in the Ada Program Office opined that ``obviously the Department of Defense is not interested in an artificially simplified language such as Pascal''. Modula-3 represents the opposite point of view. We used every artifice that we could find or invent to make the language simple.

C.A.R. Hoare has suggested that as a rule of thumb a language is too complicated if it can't be described precisely and readably in fifty pages. The Modula-3 committee elevated this to a design principle: we gave ourselves a ``complexity budget'' of fifty pages, and chose the most useful features that we could accommodate within this budget. In the end, we were over budget by six lines plus the syntax equations. This policy is a bit arbitrary, but there are so many good ideas in programming language design that some kind of arbitrary budget seems necessary to keep a language from getting too complicated.

In retrospect, the features that made the cut were directed toward two main goals. Interfaces, objects, generics, and threads provide fundamental patterns of abstraction that help to structure large programs. The isolation of unsafe code, garbage collection, and exceptions help make programs safer and more robust. Of the techniques that we used to keep the language internally consistent, the most important was the definition of a clean type system based on a subtype relation. There is no special novelty in any one of these features individually, but there is simplicity and power in their combination.