Getting Clojure

In the Wild

If it seems like macros might be one of those advanced programming features, something that you aren’t likely to have a lot of contact with until you get really good at the language, well, no. Certainly, you can—and probably should—do a lot of Clojure programming without writing any macros. But there’s no avoiding macros because much of the familiar core of Clojure is actually made of macros.

Here, for example, is a somewhat cut-down version of Clojure’s own when:^[34]

(defmacro when
  [test & body]
  (list 'if test (cons 'do body)))

And here’s the rather more complicated cond:

(defmacro cond
  [& clauses]
    (when clauses
      (list 'if (first clauses)
            (if (next clauses)
                (second clauses)
 (throw (IllegalArgumentException. ...