Scope and Extent

Scope refers to the way in which named entities such as variables, labels, types and procedures are controlled in their ability to have an effect in a program. To be more specific, the scope of a name is that part of the program text where all uses of the name are the same. This concept should not be confused with the related but distinct concept called extent which is the time during execution that the storage used to hold a variable’s value is bound to its name. In this chapter we study both of these notions. As scope and extent have long been recognized as essential issues of programming languages, they have been discussed in many texts before. Similar and more detailed treatments can be found in [Wulf 81 and Tennent 81].