Allegro CL Express 8.1 on Linux x86 enters sldb in slime 09-10-01 when a unicode character name is entered. Example:

CL-USER> #\greek_small_letter_lambda
Error: Recursive error while printing or signalling an error.
       This is sometimes caused by an error in a print-object
       method.

Restart actions (select using :continue):
   0: Return to sldb level 99.
   1: Return to sldb level 98.
   2: Return to sldb level 97.
..........
  95: Return to sldb level 4.
  96: Return to sldb level 3.
  97: Return to sldb level 2.
  98: Return to sldb level 1.
  99: Retry SLIME REPL evaluation request.
 100: Return to SLIME's top level.
 101: Abort entirely from this (lisp) process.
[Current process: repl-thread]
[1] CL-USER(1): :res

Warning: stream-unread-char: ignoring #\null (expected #\:)

Relevant settings:

(setq slime-net-coding-system 'utf-8-unix)
(setq slime-lisp-implementations
      '((allegro ("/usr/local/acl81.express/alisp")
         :coding-system utf-8-unix)
    (sbcl ("/usr/local/sbcl/bin/sbcl")
          :env ("SBCL_HOME=/usr/local/sbcl/lib/sbcl")
          :coding-system utf-8-unix)))

Regards, /S