Revisiting extensions to Modula-2 to support reusability

J. Börstler, A. Zündorf

	   Achieving reusability is a central goal in programming. Since
	   code can seldom be reused "as-is", it is advantageous
	   to have language concepts that help in adapting code to
	   different needs. In modern programming languages reuse is
	   supported by constructs for encapsu- lation, genericity,
	   and inheritance. But most programming languages in use do not
	   support all of these facilities. It is therefore interesting
	   to study how these languages can be used or maybe ex- tended
	   to support reuse.

	   We have chosen Modula-2 for this discussion for several
	   reasons: (a) the recent discussion about this topic in the
	   literature, (b) our own experiences, and (c) the simplicity of
	   the language.  It is our persuasion that most of the discussion
	   can simply be transferred to other (procedural) languages.

	   In this paper we review solutions for Modula-2 proposed
	   in the li- terature. In addition we also present our own
	   variations and ex- tensions to these solutions. We classify
	   these solutions into so- lutions without changing the language,
	   and solutions which extend Modula-2 in some way. Since Modula-2
	   is a strongly typed language without explicitly supporting
	   genericity and/or inheritance, it is difficult to write really
	   reusable code (e.g. generic abstract data types). Therefore,
	   Modula-2 contains constructs for by-passing the type checking
	   (ADR(...), ADDRESS, ARRAY OF BYTE/WORD). These con- structs
	   can be used to introduce adaptability.

	   Several examples are presented to clarify our ideas.