:: Ord a => [a] -> [a] -package:html-entities -package:basement -package:Cabal -package:witherable -package:containers -package:lifted-base -package:statistics -package:imports -package:Cabal-syntax -package:generic-deriving -package:hxt -package:vector-algorithms 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.