[racket] trouble debugging - please help

On Sun, Jan 9, 2011 at 5:50 PM, Lewis Brown <lewisbrown at gmail.com> wrote:
>
> The error is:
>
> string-length: expects argument of type <string>; given #"\0"
>
> There is one instance of this call in the program, so it is easy to know that the early fail is not due to either expansion or execution of this code. What else could it be and how do I fix it?

That's not the error I get. I get this:

Welcome to DrRacket, version 5.0.99.6--2011-01-09(d2cb96bc/d) [3m].
Language: racket; memory limit: 128 MB.
. expand: unbound identifier in module (in phase 1, transformer
environment) in: a
>

And I'm pretty sure this isn't a version difference. I'm pretty sure
that'd be an unbound identifier in most versions of Racket. It is
referring to the body of the function monitored-port where the binding
of 'len' uses 'a'.

Robby