(deftype valid-comchar ()
  "Usable characters for irc comchars.

Most anything else in the ASCII set can't be used as they occur as part
of normal conversation and an IRC bot that interferes with that is not
a very friendly bot."
  '(member #\! #\# #\% #\) #\+ #\, #\- #\.
    #\@ #\\ #\] #\_ #\` #\{ #\| #\} #\~))