Hi all, I'm struggling to figure out how to catch an exception in Haskell. Eventually, what I want to do is to use the Control.Macho library (from Hackage) to parse binaries on Mac OS X. Naturally, I would like my program to gracefully handle corrupted files or files that aren't binaries. So I need to catch exceptions if the parsing with Data.Macho fails... This is what I've got so far: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=1877#a1877 Digression: Note that if I leave out the `foo e` call, then I get scratch.hs:21:9: Ambiguous type variable `e' in the constraint: `Exception e' arising from a use of `try' at scratch.hs:21:9-11 Probable fix: add a type signature that fixes these type variable(s) I find this somewhat counter-intuitive; this is also not discussed in the book "Real-World Haskell" (at least I haven't found it), which is what I'm using to learn Haskell. What is the best way to get around this? Back to my problem. The program produces the following output: $ runghc scratch.hs Testing Pure... Caught a bad exception: abort via error Testing Macho... No exception occured, the result is: scratch.hs: too few bytes. Failed reading at byte position 4 This counter-intuitive in at least two ways: 1) How can it fail at position 4 in an empty string? That looks like a sloppy error message too me; why doesn't it report the actually failing position? 2) Why can I catch an exception raised with an error in my own code, but not the one raised by Data.Binary.Get? Looking at http://hackage.haskell.org/packages/archive/binary/0.5/doc/html/src/Data-Bin... , an exception within Data.Binary.Get is also raised with error. What is the difference? Why am I seeing what I'm seeing, and how should I be doing it in the first place? Thanks in advance, Bjoern