I definitely think that shunting stderr to stdout, or any other method of displaying errors would make a huge difference.
I agree with you and am working on it. The only reason I've hesitated with that feature is that certain errors reveal information about the sandboxing mechanism I'm not sure I want people to have.
arc> (system "ls")
subprocess: `execute' access denied for /bin/sh
Maybe it's not really an issue at all, but it is something I've worried about. I could probably hedge my bets by displaying more generic error messages than the ones the sandbox provides.
Other than that, it's really rather cool. Great job!
