Should I avoid using Monad fail?

Question

I\'m fairly new to Haskell and have been slowly getting the idea that there\'s something wrong with the existence of Monad fail. Real World Haskell warns against its use (\"Once

Answer 1

I try to avoid Monad fail wherever possible, and there are a whole variety of ways to capture fail depending on your circumstance. Edward Yang has written a good overview on his blog in the article titled 8 ways to report errors in Haskell revisited.

In summary, the different ways to report errors that he identifies are:

1. Use error
2. Use Maybe a
3. Use Either String a
4. Use Monad and fail to generalize 1-3
5. Use MonadError and a custom error type
6. Use throw in the IO monad
7. Use ioError and catch
8. Go nuts with monad transformers
9. Checked exceptions
10. Failure

Of these, I would be tempted to use option 3, with Either e b if I know how to handle the error, but need a little more context.