Question

I have a function that returns type ErrorT String IO (). While the function works, liftIO‘s litter every line that does IO. It makes for a mess. Is there any way to get around this and still have the ability to abort on error?

Answer 1

I assume this is the context of the question, so I’ll repost the comment I left over there in case you didn’t notice it:

If you use a few particular functions a lot, you could write a wrapper around them, e.g. liftedPutStr = liftIO . putStr. You could even import the originals qualified and make your lifted version use the same name, if you wanted. Also, a group of IO actions that won’t raise errors can be pulled out into a single, separate function that can then be liftIOd just once. Does that help?

In case you’re not familiar with qualified imports, here’s putStr again as an example:

import Prelude hiding (putStr)
import qualified Prelude as P
import Control.Monad.Trans

putStr x = liftIO $ P.putStr x

That should let you use the altered putStr in a transformed IO the same way you’d normally use the real putStr in plain IO.