MVEL validates illegal expressions using ":" -------------------------------------------- Key: DROOLS-452 URL: https://issues.jboss.org/browse/DROOLS-452 Project: Drools Issue Type: Bug Reporter: Davide Sottara Assignee: Petr Široký Priority: Minor Fix For: 6.4.x A rule like this {code} rule "Typo" dialect "mvel" when ... then // Notice the ":" in place of ";". There is also a \n at the end of the line System.out.println( "Hello" ): // more statements here end {code} MVEL will validate the RHS at compile time. At runtime, the printout (actually any statement ending with ":") will be executed, but MVEL will fail silently thereafter. The rest of the conclusion will not be evaluated.