In the latest snapshot (dpsearch-4.54-15042011.tar.bz2, as well in trunk version in the SVN repository), the search daemon searchd of DataparkSearch Engine has got the RESTful interface, though it support only the GET command at the moment.
It's simple to use it: open a TCP connection on searchd port (7003 by default), and send a query in the following format:
GET query_string
where to put usual QUERY_STRING of the CGI as it comes when you query via search.cgi instead of "query_string", and you get search results filled accordingly to the search template (search.htm by default or that specified in tmplt CGI-parameter).
NB: Similar to mod_dpsearch module for Apache, you don't need to specify DBAddr commands in the template used with RESTful interface, the same for commands related to synonyms, acronyms, stopwords, etc. If you have specified such commands in your searchd.conf config file, they are used to perform queries come via RESTful interface.
PS: It seems it become very easy to build search API to DataparkSearch Engine in computer languages. 🙂