Mastering Clojure Macros

Turning Expressions Inside Out with Threading Macros

Some of Clojure’s most fun built-in macros are the ones that allow you to rewrite deeply nested expressions in a way that more closely reflects their execution order. In this section, we’ll take a look at how we can use these threading macros to simplify our code and how those macros work their magic. And to avoid confusion: threading in this context has nothing to do with JVM/OS threads; the two concepts just have an unfortunate naming collision.

The most common of these macros is ->, which threads the result of each expression into the next one as the first argument (converting symbols to lists where the next expression is not a list). Perhaps you’ve seen this macro before, when composing ...