:: Ord a => [a] -> [a] -package:hspec -is:exact -package:extra -package:mono-traversable -package:ghc -package:containers -package:vector-algorithms -package:lifted-base -is:exact -package:imports -is:exact package:parsers
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.