1. A program stored on a computer-readable medium that causes a computer to execute steps to determine whether a computer-storable expression matches a filter, comprising: identifying and testing the structural form of the expression; choosing a transformation model for the filter that is compatible with the structural form of the expression; evaluating a first code structure representing the expression to determine a value of said expression prior to filtering; analyzing a second code structure representing the filter to determine the characteristics of the filter, wherein the second code structure comprises a plurality of filter characteristics corresponding to a plurality of structural forms of the first code structure, the plurality of structural forms comprising text, trees, and graphs, and wherein the second code structure applies a filter corresponding to the structural form of the first code structure; and filtering said evaluated value according to the filter characteristics, wherein said first code structure is constructed from a plurality of first programming language code structure elements and said second code structure is constructed from a plurality of second programming language code structure elements, each second structure element being symmetrically constructed to correspond to one of said first structure elements, and wherein evaluating, analyzing and filtering are performed upon explicit invocation of a matching operator, and filtering comprises returning a boolean evaluation result value.