:: Ord a => [a] -> [a] -package:list-t -package:extra -package:safe -is:exact -package:ghc -package:statistics -package:mono-traversable -package:hxt -package:vector -package:witherable -package:incipit-base -package:generic-deriving 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.