+{- $catchall
+
+It is possible to catch all exceptions, by using the type 'SomeException':
+
+> catch f (\e -> ... (e :: SomeException) ...)
+
+HOWEVER, this is normally not what you want to do!
+
+For example, suppose you want to read a file, but if it doesn't exist
+then continue as if it contained \"\". You might be tempted to just
+catch all exceptions and return \"\" in the handler. However, this has
+all sorts of undesirable consequences. For example, if the user
+presses control-C at just the right moment then the 'UserInterrupt'
+exception will be caught, and the program will continue running under
+the belief that the file contains \"\". Similarly, if another thread
+tries to kill the thread reading the file then the 'ThreadKilled'
+exception will be ignored.
+
+Instead, you should only catch exactly the exceptions that you really
+want. In this case, this would likely be more specific than even
+\"any IO exception\"; a permissions error would likely also want to be
+handled differently. Instead, you would probably want something like:
+
+> e <- tryJust (guard . isDoesNotExistError) (readFile f)
+> let str = either (const "") id e
+
+There are occassions when you really do need to catch any sort of
+exception. However, in most cases this is just so you can do some
+cleaning up; you aren't actually interested in the exception itself.
+For example, if you open a file then you want to close it again,
+whether processing the file executes normally or throws an exception.
+However, in these cases you can use functions like 'bracket', 'finally'
+and 'onException', which never actually pass you the exception, but
+just call the cleanup functions at the appropriate points.
+
+But sometimes you really do need to catch any exception, and actually
+see what the exception is. One example is at the very top-level of a
+program, you may wish to catch any exception, print it to a logfile or
+the screen, and then exit gracefully. For these cases, you can use
+'catch' (or one of the other exception-catching functions) with the
+'SomeException' type.
+-}