Great Clojure Macro description!

gistfile1.txt

(C) Mikera on Stackoverflow: 
http://stackoverflow.com/questions/10434638/good-examples-of-clojure-macros-usage-which-demonstrate-advantages-of-the-langua/10435150

I find macros pretty useful for defining new language features. In most languages you would need to wait for a new release of the language to get new syntax - in Lisp you can just extend the core language with macros and add the features yourself.

For example, Clojure doesn't have a imperative C-style for(i=0 ;i<10; i++) loop but you can easily add one with a macro:

(defmacro for-loop [[sym init check change :as params] & steps]
  (cond
    (not (vector? params)) 
      (throw (Error. "Binding form must be a vector for for-loop"))
    (not= 4 (count params)) 
      (throw (Error. "Binding form must have exactly 4 arguments in for-loop"))
    :default
      `(loop [~sym ~init value# nil]
         (if ~check
           (let [new-value# (do ~@steps)]
             (recur ~change new-value#))
           value#))))
Usage as follows:

(for-loop [i 0, (< i 10), (inc i)]
  (println i))