Filter element nodes in XML with Clojure zippers

user_385505 0
Viewed 386

How can you filter text nodes in XML with Clojure zippers? For example, you may have a pretty-printed XML document that interleaves element nodes with text nodes containing whitespace:

(def doc
  "<?xml version=\"1.0\"?>
  <root>
    <a>1</a>
    <b>2</b>
  </root>")

If you want to retrieve the content of the root's children, you can do this:

(require '[clojure.data.xml :as xml]
         '[clojure.zip :as zip]
         '[clojure.data.zip :as zf]
         '[clojure.data.zip.xml :as zip-xml])

(-> doc
    xml/parse-str
    zip/xml-zip
    (zip-xml/xml-> :root zf/children zip-xml/text))

However, this returns (" " "1" " " "2" " "), including the whitespace.

How do you filter the zipper, so that only element nodes are selected?

I've come up with this.

(def filter-elements (comp (partial filter (comp xml/element? zip/node)) zf/children))

(-> doc
    xml/parse-str
    zip/xml-zip
    (zip-xml/xml-> :root filter-elements zip-xml/text))
; => ("1" "2")

I suspect it's unnecessarily complex and hence I'm looking for a better solution.

clojure xml
2 Answers

I think this relates to the general XML parsing problem of deciding which whitespace is meaningful and which isn’t. See for example this Q&A: Why am I getting extra text nodes as child nodes of root node?

I checked and found that data.xml does support skipping whitespace via an option :skip-whitespace. It’s undocumented though (source).

So best solve this at the parsing stage.

(-> doc
    (xml/parse-str :skip-whitespace true)
    zip/xml-zip
    (zip-xml/xml-> :root zf/children zip-xml/text))
; => ("1" "2")
user_3290630

You can do this using the Tupelo library, which offers XML parsing using both clojure.data.xml and tagsoup parsers:

(ns tst.demo.core
  (:use demo.core tupelo.core tupelo.test)
  (:require
    [tupelo.forest :as tf]
    [tupelo.parse.tagsoup :as tagsoup]
    [tupelo.string :as ts] ))

(dotest
  (let [doc "<?xml version=\"1.0\"?>
             <root>
               <a>1</a>
               <b>2</b>
             </root>"
        result-enlive (tagsoup/parse (ts/string->stream doc))
        result-hiccup (tf/enlive->hiccup result-enlive)
        ]
    (is= result-enlive
      {:tag   :root,
       :attrs {},
       :content
              [{:tag :a, :attrs {}, :content ["1"]}
               {:tag :b, :attrs {}, :content ["2"]}]})

    (is= result-hiccup
      [:root
       [:a "1"]
       [:b "2"]])))
user_18223790
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