rec {
   version="2.20";
   name="asymptote-2.20";
   hash="0ji45v0d9jps8clsl86pvmr22acci3f0ciicmyzak6dbczqyrj80";
   url="http://downloads.sourceforge.net/project/asymptote/${version}/asymptote-${version}.src.tgz";
   advertisedUrl="http://downloads.sourceforge.net/project/asymptote/2.20/asymptote-2.20.src.tgz";
}