Mutating XML in Clojure

Question

Clojures clojure.xml/parse, clojure.zip/xml-zip and clojure.contrib.zip-filter.xml/xml-> are excellent tools for pulling values out of xml, but what if I want to change the xml (the result of clojure.zip/xml-zip) based on what I learn from xml-> "queries" and write the result back out as xml?

I would have expected that (clojure.contrib.prxml/prxml (clojure.xml/parse xml-content)) spit back xml, but that is not the case.

Answer 1

You can use the xml-zip library to "mutate" XML just like you would any other of Clojure's immutable structures. It has a full set of "mutating" functions: (api)

They all return an entire "modified" zipper. You can then go to the top of that zipper, and user xml/emit to print the XML.

Answer 2

Update: Actually, for emitting XML, it's best to use clojure.contrib.lazy-xml/emit, because clojure.xml/emit is currently likely to break things! See my comment below.

(Leaving this answer here for now as a warning.)

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If I understand correctly, the main thrust of the question has to do with turning the (possibly mutated) XML representation back into XML text?

If so, have a look at clojure.xml/emit and clojure.xml/emit-element:

user> (with-out-str (xml/emit {:tag :foo :attrs {:bar "quux"}}))
"<?xml version='1.0' encoding='UTF-8'?>\n<foo bar='quux'/>\n"

(with-out-str captures printed output and wraps it up as a string; for some reason xml/emit prints the xml, so it comes in handy here. You'll want to use emit-element if <?xml version='1.0' encoding='UTF-8'?> is not what you want.)