I used to think that an Alternative is just an Applicative which is also a Monoid but apparently there is no consensus about this [1,2]. Actually it kind of makes sense to make the 'empty' parser fail: Consider the parser combinator choice = Data.Foldable.asum = foldr (<|>) empty which folds over a list of Alternatives. Its semantics can be regarded analogous to 'any' for a list of Booleans, and in the latter the empty list evaluates to False. Put differently: The parser (p <|> q) matches at least as many inputs than either p or q. Hence the neutral element for <|> ought to be the parser that matches the least amount of inputs, but a parser that succeeds on the empty string _does_ match some input. It would be the neutral element for the monoid operation that concatenates parsers. Olaf [1] https://en.wikibooks.org/wiki/Haskell/Alternative_and_MonadPlus [2] https://wiki.haskell.org/MonadPlus