This chapter digs deeper into how environments work and how you can evaluate expressions in different environments. Understanding how environments are chained together helps you understand how the language finds variables, and being able to create, manipulate, and chain together environments when evaluating expressions is a key trick for metaprogramming.
Expressions
You can consider everything that is evaluated in R to be an expression. Every statement you have in your programs is also an expression that evaluates to some value (which, of course, might be NULL). This includes control structures ...
