That depends on how you define an unhandled exception :) You're right of course: no compiler can guarantee lack of exceptions when it comes to IO, but I would

That depends on how you define an unhandled exception :) You're right of course: no compiler can guarantee lack of exceptions when it comes to IO, but I would argue that GHC, indeed, does verify that - unless a function explicitly throws an exception - no exception will occur. This is very different from C, where an exception can be the result of just about any operation (if you do something wrong), rather than only an effect that appears when you use "throwIO" (or similar). It's the difference between exceptions being used as a tool by the user (programmer), rather than a way for the compiler to tell the user (after your program is compiled and is running) that it has no idea what to do now, and will abort. In Haskell I write the "error"/"throwIO" statement causing an abort, in a C program I might have intended something completely different, but the compiler throws one at runtime. We mustn't mix up IO with everything else, because reality is inherently unreliable, and it's just the nature of it that a certain file won't necessarily be readable tomorrow - we can never know that. But we can know whether a pure function, sans compiler bugs, will execute without throwing an exception. And I would argue that adding "error" or "fail" does not constitute an unhandled exception, as that statement was put there intentionally by the author of the program (perhaps to test out something).