Step-debugging parsing words

With all the macro play posts, I would have gone insane by now if I had had been juggling the stack in my head.

So I wrote the equivalent of break but for parsing words. The reason why simply using break (or its always-available alias B) doesn't work for parsing words is because the walker expands them before you have a chance to step into them.
So here's B's brother, B: :

USING: definitions kernel parser tools.continuations ;
IN: syntax-break

SYNTAX: B: scan-word definition
    [ break "now press O I" drop ]
    prepose call( accum -- accum ) ;

Its definition is simple: it scans the next word, gets its definition (aka source code) as a quotation, prepends break to it, and then calls it. That's exactly what I was doing manually before I wrote this. :P

As a bonus and to be self-explanatory, I added a little "live" documentation to it (they're instructions, actually) so that I don't forget how to use it.

Oh, and I have to use call( instead of call because the quotation I'm calling isn't know at compile time.

Try it out:

IN: scratchpad "world" "hello" B: [| w h | h ", " w 3append ] call .

And then follow the instructions (hint: you'll land inside B:'s definition still, right at the "now press O I" drop part. Guess what happens when you press O and then I.)