Haskell: catching low level IO exceptions

Question

According to the System.Directory haddock, renameFile may fail with a number of reasons:

• HardwareFault A physical I/O error has occurred. [EIO]
• InvalidArgument Either operand is not a valid file name. [ENAMETOOLONG, ELOOP]
• isDoesNotExistError / NoSuchThing The original file does not exist, or there is no path to the target. [ENOENT, ENOTDIR]
• isPermissionError / PermissionDenied The process has insufficient privileges to perform the operation. [EROFS, EACCES, EPERM]
• ResourceExhausted Insufficient resources are available to perform the operation. [EDQUOT, ENOSPC, ENOMEM, EMLINK]
• UnsatisfiedConstraints Implementation-dependent constraints are not satisfied. [EBUSY]
• UnsupportedOperation The implementation does not support renaming in this situation. [EXDEV]
• InappropriateType Either path refers to an existing directory. [ENOTDIR, EISDIR, EINVAL, EEXIST, ENOTEMPTY]

A couple of these (isPermissionError, isDoesNotExistError) have testing functions, but others (including UnsupportedOperation, in which I'm interested) don't seem to correspond to anything. What is UnsupportedOperation and how can I test for it?

More generally, how should I go about finding out what something like this is. I can't see anywhere in the source code where it's raised, so I'm guessing it's a wrapper around a lower level error - but how should I deal with those?

Answer 1

UnsupportedOperation is ghc-specific. So you have to import GHC.IO.Exception, it contains everything you need to check exception type.

Here is an example:

import Control.Exception
import GHC.IO.Exception

main :: IO ()
main = do
  action `catch` (\(IOError _ UnsupportedOperation _ _ _ _) -> print "UnsupportedOperation")
  where
  action = throw $ IOError Nothing UnsupportedOperation "loc" "desc" Nothing Nothing