print-not-readable,
error,
serious-condition,
condition,
t
The type print-not-readable consists of error conditions that occur during
output while *print-readably* is true, as a result of attempting
to write a printed representation with the Lisp printer
that would not be correctly read back with the Lisp reader.
The object which could not be printed is initialized by
the :object initialization argument to make-condition, and is accessed by
the function print-not-readable-object.