VMs for Portability: BCPL

Abstract

BCPL is a high-level language for systems programming that is intended to be as portable as possible. It is now a relatively old language but it contains most syntactic constructs found in contemporary languages. Indeed, C was designed as a BCPL derivative (C can be considered as a mixture of BCPL and Algol68 plus some sui generis features). BCPL is not conventionally typed. It has one basic data type, the machine word. It is possible to extract bytes from words but this is a derived operation. All entities in BCPL are considered either to be machine words or to require a machine word or a number of machine words. BCPL supports addresses and assumes that they can fit into a single word. Similarly, it supports vectors (one-dimensional arrays) which are sequences of words (multi-dimensional arrays must be explicitly programmed in terms of vectors of pointers to vectors). Routines (procedures and functions) can be defined in BCPL and are represented as pointers to their entry points. Equally, labels are addresses of sequences of instructions.