Your errors branch has the type
writeFile "parse-errors.txt" (show errors) :: IO ()
This means that your otherwise branch should have the same type.
You can use the return function that has the type
return :: Monad m => a -> m a
specialised to m = IO
in conjunction with the value
() :: ()
giving
return () :: IO ()
There is also the when function that eliminates the else case for
conditional IO:
http://hackage.haskell.org/packages/archive/base/latest/doc/html/Control-Mon...
On Mon, Jun 20, 2011 at 4:00 PM, Dmitri O.Kondratiev
Hi, What is right way to do conditional IO? For example, I need to write to file errors only in case they exist, otherwise my function should do nothing:
handleParseErrors errors | (not . null) errors = writeFile "parse-errors.txt" (show errors) | otherwise = ?
What should be an 'otherwise' case ?
Thanks!
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