readevalprintlove / black Goto Github PK

I had read the paper, but I still dont get it after 3 hours!

So, in my understanding, eval-var should return a value, by calling k. but k is called with an old k, so eval-var return the continuation of interpreter into the current level. It than got applied with 2, which is same as having 2 as the _ value of (+ _ 1).
The continuation getting the value return 3, but at the line of (+ _ 1), because this is the old continuation, and it than continue it's own repl loop... So the line number get reset to (+ _ 1)
But why is __k away, and why is (EM (EM 'where)) meta (instead of undefined)?