Introduction to Programming Languages/Definitions and Scope Type

Let's imagine a world in which each person has a unique and different name. At first, we could think that this world would be simpler because the sentence "Paul invited Sophia to go to the party" is not ambiguous. Paul and Sophia uniquely identify two different people because there is only one Paul and only one Sophia in this world. Thinking in the other side of the same coin, it would be necessary to stablish a way of defining a distinct name for every child that born in the world. The advantages related to the uniqueness of names would be less interesting when compared to the complexity of the distinct name definition procedure.

Let's now think how we distinct people in our actual world. One way to perform this is by considering the context. Usually, the context present (implicit or explicit) in the discourse is sufficient to disambiguate the names. An example can be stated as follows: "My brother Paul invited his girlfriend Sophia to go to the party". Considering that we know the speaker and his family, we can know who is Paul and who is Sophia. Another way to disambiguate names is by adding information to they. The above statement could be rephrased as: "Paul McCartney invited Sophia Loren to go to the Oscar party". It is possible to have more than one person with the name Paul McCartney and more than one with the name Sophia Loren in the world. But the context presented above restricts the possibilities and we suggest that the man is the singer Paul McCartney and the woman is the actress Sophia Loren.

Reasons similar to the presented above make the programming languages do not insist on unique and distinct name for variables. The definition of a variable is anything that establishes an association between a name and a meaning. The following  illustrates the definition of two variables:   and.

For allowing different variables to have the same name, it is necessary to define a way of ensuring the control of the scope of definitions. This control permits the programmer to make some definitions widely visible in the program and others do not. The scope of a definition is the region of the program where that definition is valid. Programming languages specify many ways of defining a scope, such as Scoping with Blocks and Scoping with Namespaces. These two types of scoping definitions will be explained in the next section.