:: Ord a => [a] -> [a] -package:list-t -package:lens -package:Cabal -package:extra -package:basement -package:safe -package:errors -package:hxt -package:containers -package:mono-traversable -package:ghc 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.