At work our team just finished implementing a filtering library for our web services that's loosely based on OData. The query string value is parsed into an ex

At work our team just finished implementing a filtering library for our web services that's loosely based on OData. The query string value is parsed into an expression tree, then all of the operations on the expression tree are implemented using pattern matching. You could of course implement this with the visitor pattern, but in comparing the two we decided to use pattern matching because it's significantly less verbose and easier to understand.