Easy way to find out allowed data?

Hi,

Is there any convenient way to get what input qualifies as valid data
for a CHECK constraint?  I'm trying to generalise an interface which
allows data entry through the Web.  I'd like to be able to find out
what data is allowed in a field, and then generate a pick-list based
on that.  It looks like relevant information is in pg_relcheck, but
I'm not sure I understand what I'd have to do to get it out (more
like, "I'm sure I don't understand. . ."), because there's a lot of
other stuff in there.

Thanks,
A
--
Andrew Sullivan                                      Computer Services
<sullivana@bpl.on.ca>                        Burlington Public Library
+1 905 639 3611 x158                                   2331 New Street
                                   Burlington, Ontario, Canada L7R 1J4