Re: [rules-users] How to write a rule which only fires for a closest value?

Your reasoning on how to solve the problem is correct. I don't know about your implementation, but my suggestion is: 1. Create a function to calculate the distance between 2 points. I would prefer to create it as a static method in a helper class, but you can define it in the DRL if you prefer: function double distance( long originX, long originY, long actualX, long actualY ) { // return the calculated distance } 2.a. If you want to do it in a single rule, write something like this: when $a: Agent( $x1:x, $y1:y, $r:range) $t1: Tile( $x2: x, $y2 : y, eval( distance( $x1, $y1, $x2, $y2 ) <= $r ) ) not Tile( eval( distance( $x1, $y1, x, y ) < distance( $x1, $y1, $x2, $y2 ) ) ) then end The downside of such approach is that it recalculates the distance many times and the performance would be poor. 2.b. If you want best performance, try a more relational approach with 2 rules: rule "calculate distance" when $a: Agent( $x1 : x, $y1 : y, $r : range ) $t: Tile( eval( distance( $x1, $y1, x, y ) < $r ) ) then assertLogical( new TileInRange( $a, $t, distance( $x1, $y1, x, y ) ) ); end rule "find the closest" when $a: Agent() $tr TileInRange( agent == $a, $tile : tile, $dist : distance ) not TileInRange( agent == $a, distance < $dist ) $t : Tile( this == $tile ) // this last pattern may be removed if you don't need to constrain any other attribute then // do something end Hope it helps Edson 2007/12/6, velven <velven83(a)hotmail.com&gt;: -- Edson Tirelli JBoss Drools Core Development Office: +55 11 3529-6000 Mobile: +55 11 9287-5646 JBoss, a division of Red Hat @ www.jboss.com