[Haskell-cafe] converting IOException to Either in ErrorT

brian at lorf.org brian at lorf.org
Sun May 3 18:36:07 EDT 2009

I wrote this to make it a little nicer to catch IO exceptions and
convert them to ErrorT failure:

  :: (Error ce) =>
     IO a
  -> (String -> ce)
  -> ErrorT ce IO a
onExceptionThrowError a ce =
    liftIO (try a) >>=
        (\(e :: IOException) -> throwError (ce (show e)))

So now I can do, e.g.,
writeFile fp s `onExceptionThrowError` SpecificErrorConstructor ...

It works, but seems bad. Please let me know if you see ways to improve
it. Thanks.

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