Adapting Modula-2 for distributed systems

Modula-2 is a recently developed concurrent programming language designed primarily for implementation on a mono-processor. This paper reports on the changes found necessary, both to the source language and to the support environment, in order to allow the language to be used to program a tightly coupled, homogenous, distributed computing system. Specific areas covered are: the allocation of program code and data to processors, which is kept independent of the source code, allowing flexible re-allocation without re-compilation; the choice of an inter-processor communication mechanism, where the remote procedure call was considered to be the most flexible technique; and the selection of an inter-process communication mechanism, where, despite the distributed nature of the target, the monitor was found most suitable.