The JSONResponseWriter class currently supports several styles of NamedList output format, documented on the wiki at http://wiki.apache.org/solr/SolJSON and in the code at https://github.com/apache/lucene-solr/blob/master/solr/core/src/java/org/apache/solr/response/JSONResponseWriter.java#L71-L76.
For example the 'arrmap' style:
This patch creates a new style ‘arrnvp’ which is an array of named value pairs. For example:
This style maintains the type information of the values, similar to the xml format: