Hmm. It might be related but I somehow doubt it. The buggy program is ------------------------------------------ module Bug2 where data Bug2 = Bug2 instance Show Bug2 where showsPrec _ Bug2 str = showChar '?' str ------------------------------------------ (stack overflow on Bug2> Bug2) and the fix is ------------------------------------------ module Bug2 where data Bug2 = Bug2 instance Show Bug2 where showsPrec _ Bug2 str = showChar '?' str ------------------------------------------ -- an indentation problem. Quite why globally redefining showsPrec produces a stack overflow when showing Bug2 values I'll have to leave to the experts. --------------------------------------------------------------------------- Matt Fairtlough m.fairtlough@dcs.shef.ac.uk Verification and Testing Group Room 115 Department of Computer Science University of Sheffield Regent Court, 211 Portobello Street Sheffield S1 4DP Tel: (0)114-22-21826 UK Fax: (0)114-22-21810 WWW: http://www.dcs.shef.ac.uk/~matt/ ----------------------------------------------------------------------------