Question

I am a Clojure n00b trying to create some XML strings.

My goal is to create something like this:

<?xml version="1.0" encoding="UTF-8"?>
<items>
  <item name="n0">n0 value</item>
  <item name="n1">n1 value</item>
  <item name="n2">n2 value</item>
</items>

I can use the clojure.data.xml library’s element function directly like this:

(element :items {} 
  (element :item {:name "n0"} "n0 value")
  (element :item {:name "n1"} "n1 value")
  (element :item {:name "n2"} "n2 value"))

and this responds to emit-str as expected and prints the xml I am after.

The problem I am having is that I have a variable number of items for a given items collection, so I want to do something that looks like this:

(def collection-of-items 
    [(element :item {:name "n0"} "n0 value") 
     (element :item {:name "n1"} "n1 value")])

(element :items {} 
  collection-of-items)

I.e., I make a collection of several xml element objects, and give that as the :content argument for the ‘:items’ element definition.

These two forms evaluate correctly, but then emit-str fails when invoked on the result of the element invocation.

So my question is: How do I pass the ‘collection-of-items’ var to the element function as an argument so it will appear as a simple variable argument list? Or am I Missing the Clojure Boat completely here?

Thanks all!

Answer 1

Use apply:

user=> (def collection-of-items 
    [(element :item {:name "n0"} "n0 value") 
     (element :item {:name "n1"} "n1 value")])
#'user/collection-of-items
user=> (def b (apply element :items {} collection-of-items))
#'user/b
user=> b
#clojure.data.xml.Element{:tag :items, :attrs {}, :content (#clojure.data.xml.Element{:tag :item, :attrs {:name "n0"}, :content ("n0 value")} #clojure.data.xml.Element{:tag :item, :attrs {:name "n1"}, :content ("n1 value")})}
user=> (emit-str b)
"<?xml version=\"1.0\" encoding=\"UTF-8\"?><items><item name=\"n0\">n0 value</item><item name=\"n1\">n1 value</item></items>"