> you proceded by baby steps.

I call this maintainable.

> I find your approach convoluted: your sub needed the top tile to passed in

I call this flexible, it allows differing starting points

> and goal's coordinates are external global variables.

no I used lexicals,

> I do not want to be the man who has to debug your code

My fault, I expected the use of closures to be elementary. xD

Put a block around it or an extra sub ...

> You are a genial problem solver

I'm ... running out of arguments. ;-)