[Haskell-cafe] Do we need Monad fail (or MonadFail)?

Monads seem to use fail in one of three ways: -Regular monads leave it at the default definition of error -MonadPlus sometimes redefines it to mzero -IO redefines it to failIO Are there any other definitions of fail? If not, does the special case of IO really need a class-level definition, or could there be another way of dealing with failed pattern matches?