Zipping XML with Clojure
I've written about parsing XML with Clojure before, the problem is, as I wanted more from the document, loops started to get uglier. I thought it was time to try the zip-filter API, it provides XPath style navigation in Clojure. Not much documentation about it exists but as usual source code was very helpful.
We begin by including the required libraries,
(ns zp (:require [clojure.zip :as zip] [clojure.xml :as xml]) (:use clojure.contrib.zip-filter.xml))
And a utility function to convert a XML string into a zip structure,
(defn zip-str [s] (zip/xml-zip (xml/parse (java.io.ByteArrayInputStream. (.getBytes s)))))
I was playing with the XML example snippet from Wikipedia, which it claims has all the XML concepts in it.
(def paintings (zip-str "<?xml version='1.0' encoding='UTF-8'?> <painting> <img src='madonna.jpg' alt='Foligno Madonna, by Raphael'/> <caption>This is Raphael's 'Foligno' Madonna, painted in <date>1511</date>-<date>1512</date>.</caption> </painting>"))
xml-> call provides a way to navigate through the elements and attributes in an XML document. If we want to access the caption tag we can use,
(xml-> paintings :caption text)
Or to get the dates it was painted in,
(xml-> paintings :caption :date text)
For accessing attributes, there is the attr function which returns the matching XML attribute,
(xml-> paintings :img (attr :src))
These calls return a sequence, you can either call first on them or use the xml1-> function, which calls it for you. zip-filter can do more than these simple examples, these are what I needed at the moment for more examples, have a look at the bottom of the source code.