Control Abstraction

The concept of abstraction is a recurrent theme in this text. Right from the first chapter, we have encountered abstract machines and their hierarchies. For them, we used the terms “abstract” as opposed to “physical”, denoting by abstract machine, a set of algorithms and data structures not directly present in any specific physical machine, but executable on it by means of interpretation. Moreover, the fact that the concept of abstract machine, to some extent, hides the underlying machine is fundamental.