Work In Process isn’t just code sitting in your editor. It’s any task that’s not done, done, done. In other words, if it hasn’t made it all the way through your software process, it’s still work in process.
I have heard several talks and attended several presentations both comparing Scrum and Kanban and explaining how they can be used together. I came across this article, which talks about this article (I list both because the commenting article brings up good points, too). So why am I adding yet another level of indirection to this chain? Because an awful lot of people understand past the surface and the buzzwords of the various flavors of Agile/Lean, and that leads to confusion, unmet expectations, and failed projects. The most important point of these articles is that Scrum and Kanban are not interchangeable techniques. They differ greatly in scope and goal. That’s why they bring up the metaphor of choosing between a knife and fork.