The invention provides a pattern matching technique based on the symmetrical construction of the code structures representing the matching expression and the filter to be matched. The method of the invention is for determining whether a computer-storable expression matches a filter. A first code structure representing the expression is evaluated for determining a value of the expression. A second code structure representing the filter is analyzed for determining the characteristics of the filter. Then, the value is filtered according to the filter characteristics. The first code structure is constructed from a plurality of first programming language code structure elements and the second code structure is constructed from a plurality of second programming language code structure elements. Each second structure element corresponds to one of the first structure elements. This symmetrical construction of both code structures enables an arbitrary level of structural complexity. The matching operation may be invoked explicitly.