Abusing NSPredicate

Dave DeLong:

One of the best things about NSPredicate is its parsing engine. Given a well-formatted NSString, NSPredicate will turn it into a tree of NSCompoundPredicate and NSComparisonPredicate objects. This can be used to our advantage. If we have a string that represent some boolean expression, we can tap NSPredicate to parse it for us and give us back an organized syntax tree.