:: Ord a => [a] -> [a] -package:hspec -package:Cabal -package:lens -package:ghc -package:lifted-base -package:integration -package:base -is:exact is:exact -package:extra -package:Cabal-syntax 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.