Functions on the LHS are not advised and says so in the drools user guide. I can think of two ways to do this (forgive me if my syntax is slightly off). Way number 1 rule "ProductDescription validation" when $listing : Listing( $description:productDescription != null, description.title != null ) then ListingScrubber listingScrubber = new ListingScrubber(listing); insert(listingScrubber); end rule "ProductDescription validation Part 2" when $listingScrubber : ListingScrubber(forbiddenWordInTitle == true , $title: productDescription.title) then String word = $listingScrubber.getWord(); System.out.println("ERROR: " + word); end Way number2 rule "ProductDescription validation" when $listing : Listing( $description:productDescription != null, $title : productDescription.title != null) then List<ListingWord> listingWordList = listing.getListingWords(); Iterator<ListingWord> listingWordListIter = listingWordList.iterator(); while(listingWordListIter.hasNext()) { ListingWord listingWord = listingWordListIter.next(); assert(listingWord); } end $word : hasForbiddenWordsSet( wordsSet, $description.getTitle() ) rule "ProductDescription validation Part 2" when $badWordList : BadWordList($wordList : list) $listingWord : ListingWord($word : word memberof $wordList, $listing : listing) then System.out.println($listing.productDescription + " has naughty word:" + $word); End Hi! I'm new here and a have a doubt about rules and functions in Drools. I have this rule: rule "ProductDescription validation" when $listing : Listing( $description:productDescription != null ) eval( $description.getTitle() != null ) eval( hasForbiddenWordsSet( wordsSet, $description.getTitle() ) ) then System.out.println("ERROR!"); end And this function: function boolean hasForbiddenWordsSet(Set wordsSet, String value) { #do something useful here } And everything works fine. But now I want that function "hasForbiddenWordsSet" return a String. For example to print at "then". I tried something like this: rule "ProductDescription validation" when $listing : Listing( $description:productDescription != null ) eval( $description.getTitle() != null ) $word : hasForbiddenWordsSet( wordsSet, $description.getTitle() ) then System.out.println("ERROR: " + word); end function String hasForbiddenWordsSet(Set wordsSet, String value) { #do something useful here } But it doesn't work, tried some other things and still no success. Could someone help me? Thanks in advance. -- Leandro Carvalho