cf23b8e8_All_About_Monads___HaskellWiki__Combination_strategy_for____
[Monad] Error [Type of computation] Computations which can fail or throw exceptions [Combination strategy for >>=] 
Failure records information describing the failure. Binding passes failure information on without executing the bound function, or uses successful values as input to the bound function.
All About Monads - HaskellWiki