[racket] Rosetta: Bulls and Cows / Player Implementation

I've just added the Racket implementation of Bulls and Cows / Player.
http://rosettacode.org/wiki/Bulls_and_cows/Player

Any comments and improvements are welcome.

Some comments:

I wrote a function to generate all the permutations. I couldn't find
an equivalent in the standard libraries.

The program does a minimal error checking on the user input. Parsing "
2,  5    " to (2 5) is more difficult than what I expected.

Gustavo