[Haskell-cafe] An exceptional exception
andrewcoppin at btinternet.com
Fri Nov 9 15:01:42 EST 2007
Well, my problems have now multiplied beyong belief!
Allow me to summerise:
1. There exists an I/O exception called "invalid parameter", which is
not detectable with any of the 8 predicates. (Isn't this what "illegal
operation" is supposed to be for? A general catch-all?)
2. Attempting to open an invalid filename yields the undetectable
"invalid parameter" exception (rather than, say, illegal operation).
3. Attempting to read a directory with an invalid name does the same.
3. Attempting to open a *file* you don't have permission for yields
"permission error", as expected. However, attempting to read a
*directory* yields... invalid parameter again. (Thus, even if this
exception were detectable, there's no way to tell the difference between
a permission error and a malformed filename.)
4. Not actually related to exceptions, but doesDirectoryExist "C:\"
yields False. (Even though getDirectoryContents "C:\" yields the correct
result.) So I can't even use that to filter out invalid directory names.
Clearly, making my program give the user meaningful error messages is
going to be very hard - unless I resort to trying to *parse* the output
of the Show instance for IOError...
Does anybody have any helpful hints for me at this point?
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