Update show to print an error instead of failing

These are the changes we discussed a few weeks ago, just slipped my mind, and figured I would submit them at the same time as my other PR.

 I removed the use of `fail!` in the `Show` implementation. I just changed the line that was failing with a message to print said message instead.

Note: These changes won't build without my other PR which removes uses of `move_iter()`.