Restrictive language semantics in the Multioberon system

The Oberon-based language and systems in implementation demonstrate a minimalist approach to achieving reliability, significantly different from most software systems that seek to maximize the number of supported functions. The requirements for critical systems for Category A nuclear power plants prohibit the use of even more programming practices. In order to meet the category A requirement of a stable number of iterations, the use of conditional loop operators is prohibited. To ensure ergodicity, the prohibition of the use of dynamic memory and recursion is used. A buffer overflow type vulnerability is closed by prohibiting the system operations module SYSTEM. Restrictions can be set to identify the problem of a fragile base class, type change operations, and the use of nested procedures. It is noted that the transition to the Oberon-07 dialect mainly concerned additional restrictions and fits well into the framework of restrictive semantics. Instead of languages and dialects for each set of requirements, the author proposes an approach of restrictive semantics, in which one language with a system of restrictions is used. A single RESTRICT statement has been introduced into the language as a declaration of restrictions on this module. The Multioberon compiler is implemented with one frontend, including a system of restrictions, and several replaceable backends. The syntactic analysis of the compiler is demonstrated by examples. The strategy of scaling the compiler depending on the system requirements is shown. The novelty of the restrictive semantics approach is the achievement of a set of minimum necessary properties that meet the requirements for the system. The use of the "from limitations" approach by system developers is an advantage, because it declares the really necessary properties of the system, linked to the requirements.