pretty-print bug?

[boyer@rascal.ics.utexas.edu (Bob Boyer)]

The following two transcripts show a bug in print in both KCL and AKCL
that one of Norm McCain's Lisp class students encountered.  The bug
does not arise if *PRINT-PRETTY* is NIL.

rascal% kcl
KCl (Kyoto Common Lisp)  June 3, 1987
Loading init.lsp
Finished loading init.lsp

>(setq foo '(((~ (P)) (Q)) ((~ (Q)) (P)) ((~ (P)) (~ (Q))) ((~ (P)) (P)) ((Q) (~ (Q))) ((Q) (P))))

Error: Can't pretty-print.
Error signalled by PRIN1.

Broken at PRIN1.  Type :H for Help.
>>:q

Top level.
>Bye.
rascal% akcl
AKCL (Austin Kyoto Common Lisp)  Version(1.478) Wed Jun 20 16:36:25 CDT 1990
Contains Enhancements by W. Schelter
Changes in version 1-455 definitely require recompilation of user files.
Loading init.lsp
Finished loading init.lsp

>(setq foo '(((~ (P)) (Q)) ((~ (Q)) (P)) ((~ (P)) (~ (Q))) ((~ (P)) (P)) ((Q) (~ (Q))) ((Q) (P))))

Error: Can't pretty-print.
Error signalled by PRIN1.

Broken at PRIN1.  Type :H for Help.
>>:q

Top level.
>