diff --git a/src/libutil/Makefile.am b/src/libutil/Makefile.am
index 8fab0c5b05..513d8ecf5e 100644
--- a/src/libutil/Makefile.am
+++ b/src/libutil/Makefile.am
@@ -2,7 +2,8 @@ lib_LTLIBRARIES = libutil.la
 
 libutil_la_SOURCES = util.cc util.hh hash.cc hash.hh \
  archive.cc archive.hh aterm.cc aterm.hh \
- aterm-map.cc aterm-map.hh
+ aterm-map.cc aterm-map.hh \
+ xml-writer.cc xml-writer.hh
 
 if !HAVE_OPENSSL
 libutil_la_SOURCES += \
diff --git a/src/libutil/xml-writer.cc b/src/libutil/xml-writer.cc
index 2699449095..b0e25f2c71 100644
--- a/src/libutil/xml-writer.cc
+++ b/src/libutil/xml-writer.cc
@@ -1,61 +1,6 @@
-#include <iostream>
-#include <string>
-#include <list>
-#include <map>
 #include <assert.h>
-using namespace std;
 
-
-typedef map<string, string> XMLAttrs;
-
-
-class XMLWriter
-{
-private:
-    
-    ostream & output;
-
-    bool closed;
-
-    list<string> pendingElems;
-
-public:
-
-    XMLWriter(ostream & output);
-    ~XMLWriter();
-
-    void close();
-
-    void openElement(const string & name,
-        const XMLAttrs & attrs = XMLAttrs());
-    void closeElement();
-
-    void writeShortElement(const string & name,
-        const XMLAttrs & attrs = XMLAttrs());
-    
-    void writeCharData(const string & data);
-
-private:
-    void writeAttrs(const XMLAttrs & attrs);
-};
-
-
-class XMLOpenElement
-{
-private:
-    XMLWriter & writer;
-public:
-    XMLOpenElement(XMLWriter & writer, const string & name,
-        const XMLAttrs & attrs = XMLAttrs())
-        : writer(writer)
-    {
-        writer.openElement(name, attrs);
-    }
-    ~XMLOpenElement()
-    {
-        writer.closeElement();
-    }
-};
+#include "xml-writer.hh"
 
 
 XMLWriter::XMLWriter(ostream & output)
@@ -138,6 +83,7 @@ void XMLWriter::writeAttrs(const XMLAttrs & attrs)
 }
 
 
+#if 0
 int main(int argc, char * * argv)
 {
     XMLWriter doc(cout);
@@ -159,3 +105,4 @@ int main(int argc, char * * argv)
 
     return 0;
 }
+#endif
diff --git a/src/libutil/xml-writer.hh b/src/libutil/xml-writer.hh
new file mode 100644
index 0000000000..84c7fafbc9
--- /dev/null
+++ b/src/libutil/xml-writer.hh
@@ -0,0 +1,64 @@
+#ifndef __XML_WRITER_H
+#define __XML_WRITER_H
+
+#include <iostream>
+#include <string>
+#include <list>
+#include <map>
+
+using namespace std;
+
+
+typedef map<string, string> XMLAttrs;
+
+
+class XMLWriter
+{
+private:
+    
+    ostream & output;
+
+    bool closed;
+
+    list<string> pendingElems;
+
+public:
+
+    XMLWriter(ostream & output);
+    ~XMLWriter();
+
+    void close();
+
+    void openElement(const string & name,
+        const XMLAttrs & attrs = XMLAttrs());
+    void closeElement();
+
+    void writeShortElement(const string & name,
+        const XMLAttrs & attrs = XMLAttrs());
+    
+    void writeCharData(const string & data);
+
+private:
+    void writeAttrs(const XMLAttrs & attrs);
+};
+
+
+class XMLOpenElement
+{
+private:
+    XMLWriter & writer;
+public:
+    XMLOpenElement(XMLWriter & writer, const string & name,
+        const XMLAttrs & attrs = XMLAttrs())
+        : writer(writer)
+    {
+        writer.openElement(name, attrs);
+    }
+    ~XMLOpenElement()
+    {
+        writer.closeElement();
+    }
+};
+
+
+#endif /* !__XML_WRITER_H */
diff --git a/src/nix-instantiate/main.cc b/src/nix-instantiate/main.cc
index f49615648f..f8b0f3a208 100644
--- a/src/nix-instantiate/main.cc
+++ b/src/nix-instantiate/main.cc
@@ -10,6 +10,7 @@
 #include "nixexpr-ast.hh"
 #include "get-drvs.hh"
 #include "attr-path.hh"
+#include "xml-writer.hh"
 #include "help.txt.hh"
 
 
@@ -40,21 +41,29 @@ static void printResult(EvalState & state, Expr e,
         cout << format("%1%\n") % e;
     
     else if (printArgs) {
+        XMLWriter doc(cout);
+        XMLOpenElement root(doc, "args");
+            
         ATermList formals;
         ATerm body, pos;
+        
         if (matchFunction(e, formals, body, pos)) {
             for (ATermIterator i(formals); i; ++i) {
                 Expr name; ValidValues valids; ATerm dummy;
                 if (!matchFormal(*i, name, valids, dummy)) abort();
-                cout << format("%1%: ") % aterm2String(name);
+
+                XMLAttrs attrs;
+                attrs["name"] = aterm2String(name);
+                XMLOpenElement elem(doc, "arg", attrs);
+
                 ATermList valids2;
                 if (matchValidValues(valids, valids2)) {
                     for (ATermIterator j(valids2); j; ++j) {
                         Expr e = evalExpr(state, *j);
-                        cout << format("%1% ") % showValue(e);
+                        XMLOpenElement elem(doc, "value");
+                        doc.writeCharData(showValue(e));
                     }
                 }
-                cout << format("\n");
             }
         } else
             printMsg(lvlError, "warning: expression does not evaluate to a function");