Everything in Julia is an expression that returns a value when executed. Every piece of the program code is internally represented as an ordinary Julia data structure, also called an expression. In this chapter, we will see that by working on expressions, how a Julia program can transform and even generate the new code, which is a very powerful characteristic, also called homoiconicity. It inherits this property from Lisp, where code and data are just lists, and where it is commonly referred to with the phrase: "code is data and data is code". We will explore this metaprogramming power by covering the following topics:
Expressions and symbols
Eval and interpolation
Defining macros
Built-in macros
Reflection capabilities