Reimplementing LINQ to Objects: Part 2

We're going to implement the "Where" clause/method/operator. It's reasonably simple to understand in general, but goes into all of the deferred execution and streaming bits which can cause problems. It's generic, but only uses one type parameter (which is a big deal, IMO - the more type parameters a method has, the harder I find it to understand in general). Oh, and it's a starting point for query expressions, which is a bonus.