Scope and Closures

Abstract

A scope or environment is something functions and expressions are associated with that tells them what value each variable refers to. It is used to figure out which environment expressions are evaluated in. The same variable name can be used in many places in a program, referring to different things in different locations, but the scope of an expression tells R exactly how to map names to values. In R, you have both implicit environments—that I will tend to call scopes—and explicit environments. The former is what you will use in most everyday programming, while the latter is used in more advanced techniques, which mostly add flexibility in how you can provide interfaces to users. The way that R maps names to values is the same in both settings, however, and understanding how this works can make it easier to write functions and understand advanced packages.