[rules-users] Functions invocation from condition in drools expert

Hi, I am trying to find an example where the 'when' part of the rule uses functions, I intend to include some checks on complex data structure in my considiotn. Can anyone point me to any drools/other example to illustrate how functions can be used in condition? All examples that I found have functions used in the actions part. Thanks in advance, Regards, Sameer