...

GHC 6.12's runtime handles input and output encoding, instead of simply truncating Chars; my guess is it's locale-related. And sure enough, I see several non-ASCII characters in mycology.b98 which are likely to do the wrong thing if the runtime doesn't know which character set to use.

Yup. Converting mycology.b98 to utf-8 makes it run. However, why does it run with --quiet on the original file??

That actually makes sense. That mycology Befunge source is actually a combination of Befunge-98 (which can use non-ascii characters. I'd forgotten that) and befunge-93 which uses only printable ascii characters. Without the --quiet flag, we end up inspecting a Bool value returned after taking the `length` of a row and a column, which looks to see if the grid is bigger than 80x25 characters. I guess with the --quiet flag, we ignore that Bool value and so the program never has to take the length of a line, and consequently never sees any of the non-ascii characters (because the source file is written in such a way that a befunge-93 interpreter will naturally stop execution after the '93 section of code. That also explains why simply printing the file string causes the interpreter to fail, even with --quiet. Thanks for the help,