Book Image

The Clojure Workshop

By : Joseph Fahey, Thomas Haratyk, Scott McCaughie, Yehonathan Sharvit, Konrad Szydlo
Book Image

The Clojure Workshop

By: Joseph Fahey, Thomas Haratyk, Scott McCaughie, Yehonathan Sharvit, Konrad Szydlo

Overview of this book

The Clojure Workshop is a step-by-step guide to Clojure and ClojureScript, designed to quickly get you up and running as a confident, knowledgeable developer. Because of the functional nature of the language, Clojure programming is quite different to what many developers will have experienced. As hosted languages, Clojure and ClojureScript can also be daunting for newcomers because of complexities in the tooling and the challenge of interacting with the host platforms. To help you overcome these barriers, this book adopts a practical approach. Every chapter is centered around building something. As you progress through the book, you will progressively develop the 'muscle memory' that will make you a productive Clojure programmer, and help you see the world through the concepts of functional programming. You will also gain familiarity with common idioms and patterns, as well as exposure to some of the most widely used libraries. Unlike many Clojure books, this Workshop will include significant coverage of both Clojure and ClojureScript. This makes it useful no matter your goal or preferred platform, and provides a fresh perspective on the hosted nature of the language. By the end of this book, you'll have the knowledge, skills and confidence to creatively tackle your own ambitious projects with Clojure and ClojureScript.
Table of Contents (17 chapters)
Free Chapter
2
2. Data Types and Immutability

What is a Macro?

A macro is a piece of code that is executed before your code is compiled. The code contained inside a macro call is transformed into something different and then passed on to the compiler. In Clojure, macros are defined by calling defmacro. A call to defmacro looks fairly similar to a call to defn:

(defmacro my-macro
  "Macro for showing how to write macros"
  [param]
  ;;TODO: do something
  )

Despite this apparent similarity, there is a huge difference between macros and functions. Unlike functions, macros are not called at runtime. When your program finally starts running, the macros have already been called. The code they produce has already been included in your program as if you had typed it in yourself:

Figure 11.1: Separating compile time from runtime is the key to understanding macros

Keep this idea in mind while you think about and work with macros: any macro in your code could...