XML to Json with some transformation

xml_test.clj

(ns xml_test.core
    (:require   [clojure.zip :as zip]
                [clojure.xml :as xml]
                [clj-json.core :as json])
    (:use clojure.contrib.zip-filter.xml))
	
    (defn -main [& args] 
        (let [paintings (zip/xml-zip (xml/parse "paintings.xml"))]
	   (->> (xml-> paintings :painting)		
                (map (fn [painting] { :name    (first (xml-> painting :img (attr :alt))) 
                                      :caption (first (xml-> painting :caption text))}))
                json/generate-string
                (spit "paintings.json"))))

Very nice, but what does it /mean/ ;-P