L.S., The attached program reads a filename ("x.x") from file "filenames.dat"; then the program tries to read file "x.x"; this file does not exist, in the first call to "main", an internal error message is displayed; the second time, a "file does not exist" message is displayed. The following shows what happens: __ __ __ __ ____ ___ _______________________________________________ || || || || || || ||__ Hugs 98: Based on the Haskell 98 standard ||___|| ||__|| ||__|| __|| Copyright (c) 1994-2003 ||---|| ___|| World Wide Web: http://haskell.org/hugs || || Report bugs to: hugs-bugs@haskell.org || || Version: Nov 2003 _______________________________________________ Haskell 98 mode: Restart with command line option -98 to enable extensions Type :? for help Prelude> Prelude> :l "C:\\Mijn documenten\\SoftwareOntwikkeling\\Haskell\\ReadALot\\Error InGraph.lhs" Main> main Program error: Program error: pattern match failure (181 reductions, 528 cells, 1 garbage collection) INTERNAL ERROR: Error in graph Main> Main> main Program error: x.x: IO.openFile: does not exist (file does not exist) (197 reductions, 499 cells) Main> -- Met vriendelijke groet, Herzliche Grüße, Best regards, Henk-Jan van Tuyl