I just managed to trick my experimental SPARQLScript parser into accepting simple IF-branches and placeholders. Here is an example of what is going to be possible with ARC soon (and yes, I know this snippet most probably won't excite anyone but me ;)

BASE <http://sparqlbot.semsol.org/data/>
PREFIX dc: <http://purl.org/dc/elements/1.1/>

# set the endpoint
ENDPOINT <endpoint.php>

# feed still fresh?
$current = ASK FROM <graph-updates> WHERE {
  <http://planetrdf.com/index.rdf> dc:date ?date .
  FILTER (?date > ${now-1h})
}

# refresh feed and update graph log
IF (!$current) {
  DELETE FROM <http://planetrdf.com/index.rdf>
  LOAD <http://planetrdf.com/index.rdf>
  INSERT INTO <graph-updates> { <http://planetrdf.com/index.rdf> dc:date "${now}" }
} 

(Parsed Structure)

The fun thing about the whole SPARQLScript experiment is that the parser (so far) is still below 200 LOC. A lot can be re-used from the official SPARQL Grammar, e.g. IF-blocks are really just:

Script ::= ( Query | PrefixDecl | EndpointDecl | Assignment | IFBlock )*
IFBlock ::= 'IF' BrackettedExpression '{' Script '}'

Implementing the actual SPARQLScript processing engine is of course more work than the parser, but I'm making progress there, too.