As a joke, I wrote an instance of Alternative for IO actions:

{-# LANGUAGE ScopedTypeVariables #-}

module Main where

import Control.Applicative

import Control.Exception

instance Alternative IO where

  empty = undefined

  x <|> y = handle (\ (_ :: SomeException) -> y) x

This would allow to write IO code which failsafes to a value if the previous computation failed, i.e.:

*Main Control.Applicative> undefined <|> print "Hello"

"Hello"

*Main Control.Applicative> print "Hello" <|> undefined

"Hello"

It seems a neat way to catch exception in some scenarios. What do you think? Why is not Alternative IO defined in Control.Applicative?

Thanks,

Cristiano

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