In the previous sections, you learned about lazy evaluation, copy-on-modify, and lexical scoping. These mechanisms are highly related to a type of object called environment. In fact, lexical scoping is enabled exactly by the environment. Although environments look quite similar to lists, they are indeed fundamentally different in several aspects. In the following sections, we will get to know the behavior of environment objects by creating and manipulating them, and see the way its structure determines how R functions work.
An environment is an object consisting of a set of names and has a parent environment. Each name (also known as a symbol or variable) points to an object. When we look up a symbol in an environment, it will search the set of symbols and return the object the symbol points to if it exists in the environment. Otherwise, it will continue to look up its parent environment. The following diagram illustrates...