Simultaneously process two XML files with Haskell and HXT

Question

I have two XML files that I need to parse into one record. The first document contains data for most of the record, but there is a field holds an identifier for fetching data from the second XML file, somewhat like

File 1:

<nodes>
    <node>
        <key1>value1</key1>
        <!-- etc -->
        <keyN>valueN</keyN>
        <reference>1</reference
    </node>
</nodes>

File 2:

<refs>
    <ref id="1">refValue1</ref>
    <ref id="2">refValue2</ref>
</refs>

What I would like to do is while parsing the first document, retrieving the values from the key elements, is when I extract the value of <reference>, I immediately fetch the contents of <ref id="1"> from the second file.

Since I am very new to Arrows, this is proving to be quite a challenge for me to figure out how to do. I'm able to parse the first XML file just fine, but I don't know how to pass in the second document to be used on demand.

Answer 1

At phg's suggestion, I tried parsing the second XML file into a Map first, then passing it into the parser for the first XML file. A little bit of fiddling and tweaking and I got it working.