Factor script to change case of all filenames in a directory
Comments! Comments are good, especially to people who are just learning Factor right now. Admittedly, for Factor, it's pretty readable -- I finally got it, after staring a while and doing lots of Googling -- but comments are always nice.

I can't find anything about the : name&gt;something ( etc -- etc ) word syntax online -- namely, the &gt;something part. Because of that, I'm just gonna assume that it's good syntax and move on. Alright, I finally found it! And yes, that's good syntax -- you're supposed to use a&gt;b for functions converting a to b, and that's exactly what you do. It might be better called directory-file-names&gt;upper/&gt;lower, but that's just personal preference.

It looks good, though. After figuring out how Factor works, it's pretty readable (for Factor), and actually makes me want to use the language more. Plus, as far as I can tell, you're following the official coding style to the letter. Well done.