Concepts and Semantics of Programming Languages 1

2Introduction to Semantics of Programming Languages

This chapter introduces intuitively the notions of name, environment, memory, etc., along with a first formal description of these notions. It allows readers to familiarize themselves with the semantic approach of programming that we share with a number of other authors [ACC 92, DOW 09, DOW 11, FRI 01, WIN 93].

Any high-level programming language uses names to denote the entities handled by programs. These names are generally known as identifiers, drawing attention to the fact that they are constructed in accordance with the syntactic rules of the chosen language. They may be used to denote program-specific values or values computed during execution. They may also denote locations (i.e. addresses in the memory), they are then called mutable variables. And identifiers can also denote operators, functions, procedures, modules, objects, etc., according to the constructs present in the language. For example, pi is often used to denote an approximate value of π; + is also an identifier, denoting an addition operator and often placed between the two operands, i.e. in infix position, as in 2 + 3. The expression 2 * x + 1 uses the identifier x and to compute its value, we need to know the value denoted by x. Retrieving the value associated with a given identifier is a mechanism at the center of any high-level language. The semantics of a language provides a model of this mechanism, presented – in a simplified form – in section 2.1 ...