Since macros return Clojure data structures, we will often want to return lists to represent further calls, either of functions, special forms, or other macros. Therefore, we need tools to build these lists. It’s perfectly acceptable to use the simplest tool in our toolbox, the list function:

(defmacro hello
  [name]
  (list 'println name))

(macroexpand '(hello "Brian"))
;= (println "Brian")

However, for more complex macros that return something more than a simple flat list, this quickly becomes unwieldy. This is how the source code for the standard macro while would look, written in this manner:

(defmacro while
  [test & body]
  (list 'loop []
    (concat (list 'when test) body)
      '(recur)))

The gist of this macro is lost in all the calls to list and concat.