:: Ord a => [a] -> [a] -package:html-entities -package:ghc -package:errors -package:mono-traversable -package:extra -is:exact -package:hxt -package:imports -is:exact -package:basement -package:generic-deriving package:parsers -is:exact
Take a parser that may consume input, and on failure, go back to where
we started and fail as if we didn't consume input.