:: Ord a => [a] -> [a] -package:html-entities -package:witherable -package:statistics -package:base -package:ghc -package:Cabal-syntax -package:lifted-base -package:generic-deriving -package:incipit-base -package:errors -package:basement -package:extra 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.